IDEA: hidden image finder

[agentsteal]

Could someone make a program that can test whether an image contains a resized, transparent version of another image? The images I need to test contain hidden images that can't easily be found because they are almost completely transparent.

For example, the program could take this image:
http://pro.corbis.com/images/42-21127424.jpg?size=67&uid={a5b3f817-e953-4276-9eb7-8c980d4f9a13}
and this watermark:
http://cachens.corbis.com/pro/logo.gif
and would calculate that it is probable that a version of the watermark is in the image.

Thanks!

[r0bertdenir0]

Speaking from a gut feel I don't think this is possible unless you understand the algorithm that overlaid the 2 images in the first place.
There are literally countless ways to do create a watermark this way.
Basically you can just make a translucent image & overlay it on the original.
But I'm sure you would find cases in which this results in something undesirable & so the programmers probably fine tuned the method to cope with this.
So I'd say it can be done but yr best chance would be if you had detailed info about the source code algorithm.

[r0bertdenir0]

It just occurred to me there may be another way...
When the watermarked image is created in this way, there's a good chance (with sites like corbis) that the software writes some specific metadata that you can read.
Like if if conforms to the EXIF standard - maybe there's a "Copyright blahblah Ltd." in some field that you can search for.