I am looking for an EASY way to check if an image is a scaled version of another image. It does not have to be very fast, it just should be "fairly" accurate. And written in .NET. And for free.

I know, wishful thinking :-)

I am pretty sure, even without having tried it, that converting the bigger image to the smaller scale and comparing checksums is not working (especially if the smaller version was done with another software then .NET).

The next approach would be to scale down and compare pixels. But first of all, it seems like a really bad idea running a loop over all pixels with a bool comparison results, I am sure there will be some pixels off by a bit or so...

Any library coming to mind? Way back in the university we had some MPEG7 classes, so I am thinking about using a combination of "statistics" like tone distribution, brightness, etc..

Any ideas or links for that topic?

Thanks,
Chris