question regarding image processing

Hi,

I'm not sure if this is the right group to ask. I am developing a
small image library and I don't know how to hide the actual path to
the image. So I go to the stock photo library websites to see how they
hide their images. This is what I see from gettyimages.com

<img src="http://cache2.asset-cache.net/xc/200186170-001.jpg?
v=1&amp;c=NewsMaker&amp;k=2&amp;d=1EF4EE1EFB3A2CD3 E55FD7668143826B10621193DB58D674"
id="ctl12_ctlComp_imgThumb" class="thumbHeight">

Can someone please explain why there are parameters after the ".jpg",
which is not an executable file? I've got the link by right-click and
view image properties. However, if I just copy the link, and paste
into a new window, I won't see the image.

Any one knows what technique is this?

Thank you.
DP.

..oO(DP)

>I'm not sure if this is the right group to ask. I am developing a
>small image library and I don't know how to hide the actual path to
>the image. So I go to the stock photo library websites to see how they
>hide their images. This is what I see from gettyimages.com
>
><img src="http://cache2.asset-cache.net/xc/200186170-001.jpg?
>v=1&amp;c=NewsMaker&amp;k=2&amp;d=1EF4EE1EFB3A2CD 3E55FD7668143826B10621193DB58D674"
>id="ctl12_ctlComp_imgThumb" class="thumbHeight">
>
>Can someone please explain why there are parameters after the ".jpg",
>which is not an executable file? I've got the link by right-click and
>view image properties. However, if I just copy the link, and paste
>into a new window, I won't see the image.

Simple copy & paste won't work, since the link contains character
references (&amp;), which are required for HTML. Try this one to get the
image:

http://cache2.asset-cache.net/xc/200...621193DB58D674

>Any one knows what technique is this?

Just because you see a .jpg in the URL doesn't necessarily mean it is an
image. It can be anything else, in this case it could be a script that
returns an image based on the passed parameters.

Remember: a URL is just a string, nothing more. Things like "directory"
or "file extension" don't have a real meaning there. It's completely up
to server to decide what to do with something like ".jpg" at the end.

Micha

On 20 May, 23:47, DP <ldpha...@gmail.com> wrote:
> Hi,
>
> I'm not sure if this is the right group to ask. I am developing a
> small image library and I don't know how to hide the actual path to
> the image. So I go to the stock photo library websites to see how they
> hide their images. This is what I see from gettyimages.com

I'm not sure what you're after doing here. Hiding the path to an image
is not the same thing as hiding an image. If you hide an image, no one
can see it. If you allow someone to see it (on their browser), they
already have the image on their machine, in which case there is no
point in hiding the "path". I sometimes store images in a database
table, so there is no "path" as such.

If you want people to be able to see your images on their browser but
not to be able to keep a copy of them, forget it. There was a long
discussion about this recently. The bottom line is that the only thing
you can do to stop folks having a useful copy on their machine is to
put a watermark on the pictures.

Thanks Michael & Captain. I know that Apache httpd.conf can be set to
execute any extension (I just know the fact). I just don't know that
they use what technique to return the image. I have a few assumptions,
but don't know which one is best:

1. the '.jpg' is an executable script, and it reads the image data
from original image file in file system, adds watermark, and outputs.
Or it can read data from watermarked image (watermarked image is
created from upload time). Then what happens if I need to display 50
images in one page? the script only processes one by one.

2. Images (and maybe watermarked images & thumbnails) are stored in
database. The script just returns data. I don't like this approach
because if I have hundreds of thousands of images, database is
probably not a good choice (from some discussions about storing images
in db vs. file system)

On May 20, 4:47 pm, DP <ldpha...@gmail.com> wrote:
>
> I'm not sure if this is the right group to ask. I am developing a
> small image library and I don't know how to hide the actual path to
> the image. So I go to the stock photo library websites to see how they
> hide their images. This is what I see from gettyimages.com
>
> <img src="http://cache2.asset-cache.net/xc/200186170-001.jpg?
> v=1&amp;c=NewsMaker&amp;k=2&amp;d=1EF4EE1EFB3A2CD3 E55FD7668143826B10621193DB58D674"
> id="ctl12_ctlComp_imgThumb" class="thumbHeight">
>
> Can someone please explain why there are parameters after the ".jpg",
> which is not an executable file?

Who knows... Maybe the parameters are just for logging and have no
use in
the actual application. Maybe the server is configure to rewrite
URLs...

> I just copy the link, and paste into a new window, I won't see the image.
>
> Any one knows what technique is this?

There is no technique. Try replacing "&amp;" with "&":

http://cache2.asset-cache.net/xc/200...621193DB58D674

The file is perfectly visible...

Cheers,
NC

..oO(DP)

>Thanks Michael & Captain. I know that Apache httpd.conf can be set to
>execute any extension (I just know the fact). I just don't know that
>they use what technique to return the image. I have a few assumptions,
>but don't know which one is best:
>
>1. the '.jpg' is an executable script, and it reads the image data
>from original image file in file system, adds watermark, and outputs.
>Or it can read data from watermarked image (watermarked image is
>created from upload time). Then what happens if I need to display 50
>images in one page? the script only processes one by one.

Each image request is independent from each other and will start another
instance of the script on the server. In theory 50 requests would invoke
the same script 50 times, but in practice this won't happen because of
some default limits each web server has. Usually at most 2 or 4 requests
from the same client to the same host are answered in parallel, all
others are delayed. The same happens with static files as well.

>2. Images (and maybe watermarked images & thumbnails) are stored in
>database. The script just returns data. I don't like this approach
>because if I have hundreds of thousands of images, database is
>probably not a good choice (from some discussions about storing images
>in db vs. file system)

The real issue will be the same as with #1: You have to call a script
for each image. That's the main impact to the overall site performance.
Whether the images are stored on disk or in a DB is more a question of
personal preference, although DB storage may slow things down even more
in such a case (50 script calls, 50 DB connections, 50 data transfers
from the DB to the script).

Micha

DP escribió:
> 1. the '.jpg' is an executable script

Actually, you have no way to find out where the URL points to. With
modules like Apache's mod_rewrite you can make
http://example.com/foo/bar.jpg?a=1&b=1 point to
http://example.com/scripts/do-fancy-stuff.php?x=2 and it'll be
completely invisible to site visitors.


> Then what happens if I need to display 50 images in one page? the script only processes one by one.

That's true even with regular JPEG files: one file, one picture. God
bless caching, queueing and multitasking ;-)


> 2. Images (and maybe watermarked images & thumbnails) are stored in
> database. The script just returns data. I don't like this approach
> because if I have hundreds of thousands of images, database is
> probably not a good choice (from some discussions about storing images
> in db vs. file system)

Some guys adore storing binary data in databases but of course that's a
good old discussion. I particularly find no benefits in it (you can't do
searches like "WHERE category_id=20 AND picture PORTRAITS A 'black
cat'") and it add an annoying overhead in all related tasks.


--
-- http://alvaro.es - Álvaro G. Vicario - Burgos, Spain
-- Mi sitio sobre programación web: http://bits.demogracia.com
-- Mi web de humor al baño María: http://www.demogracia.com
--

Michael Fesser wrote:
> .oO(DP)
>
>> Thanks Michael & Captain. I know that Apache httpd.conf can be set to
>> execute any extension (I just know the fact). I just don't know that
>> they use what technique to return the image. I have a few assumptions,
>> but don't know which one is best:
>>
>> 1. the '.jpg' is an executable script, and it reads the image data
>>from original image file in file system, adds watermark, and outputs.
>> Or it can read data from watermarked image (watermarked image is
>> created from upload time). Then what happens if I need to display 50
>> images in one page? the script only processes one by one.
>
> Each image request is independent from each other and will start another
> instance of the script on the server. In theory 50 requests would invoke
> the same script 50 times, but in practice this won't happen because of
> some default limits each web server has. Usually at most 2 or 4 requests
> from the same client to the same host are answered in parallel, all
> others are delayed. The same happens with static files as well.
>
>> 2. Images (and maybe watermarked images & thumbnails) are stored in
>> database. The script just returns data. I don't like this approach
>> because if I have hundreds of thousands of images, database is
>> probably not a good choice (from some discussions about storing images
>> in db vs. file system)
>
> The real issue will be the same as with #1: You have to call a script
> for each image. That's the main impact to the overall site performance.
> Whether the images are stored on disk or in a DB is more a question of
> personal preference, although DB storage may slow things down even more
> in such a case (50 script calls, 50 DB connections, 50 data transfers
> from the DB to the script).
>
> Micha

If you have a large number of images, a database is often faster than
the file system. Databases can easily handle 100K images; file systems
not so much.

--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
==================

Álvaro G. Vicario wrote:
> DP escribió:
>> 1. the '.jpg' is an executable script
>
> Actually, you have no way to find out where the URL points to. With
> modules like Apache's mod_rewrite you can make
> http://example.com/foo/bar.jpg?a=1&b=1 point to
> http://example.com/scripts/do-fancy-stuff.php?x=2 and it'll be
> completely invisible to site visitors.
>
>
>> Then what happens if I need to display 50 images in one page? the
>> script only processes one by one.
>
> That's true even with regular JPEG files: one file, one picture. God
> bless caching, queueing and multitasking ;-)
>
>
>> 2. Images (and maybe watermarked images & thumbnails) are stored in
>> database. The script just returns data. I don't like this approach
>> because if I have hundreds of thousands of images, database is
>> probably not a good choice (from some discussions about storing images
>> in db vs. file system)
>
> Some guys adore storing binary data in databases but of course that's a
> good old discussion. I particularly find no benefits in it (you can't do
> searches like "WHERE category_id=20 AND picture PORTRAITS A 'black
> cat'") and it add an annoying overhead in all related tasks.
>
>

The ability to search is not the only reason to store things in
databases. And if you have hundreds of thousands of images, a database
can be more efficient.

--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
==================

Jerry Stuckle escribió:
> If you have a large number of images, a database is often faster than
> the file system. Databases can easily handle 100K images; file systems
> not so much.

If you mean "in the same directory", you're absolutely right.


--
-- http://alvaro.es - Álvaro G. Vicario - Burgos, Spain
-- Mi sitio sobre programación web: http://bits.demogracia.com
-- Mi web de humor al baño María: http://www.demogracia.com
--