Can Anybody ?

If the pictures are exactly the same, any file duplicate detector will do the job, e.g., rdfind or fdupes (both are in Trisquel's repository). There exits some graphical interface to such commands (and others). FSlint, for instance, is in Trisquel's repositories.

If the images were modified (e.g., resized), take a look at findimagedupes, which is in Trisquel's repository too.

The GNU Image-Finding Tool ( GIFT ) may be of use for duplicate photos of different file type.

http://www.gnu.org/software/gift/

Package names in Trisquel :

gnuift
gnuift-doc

I have used fdupes for this with good success.

I had a lot of duplicate due to the fact that I stored multiple folders keeping my handy pics and movies. This resulted in a waste of space.

Benefit of fdupes about other tools IMO: It also can process movies which might be often part of camera specific content.

Disadvantage so far I found:
fdupes asks for any found duplicates for manual input. I found a trick to get around this and only keep the first file:
yes 1 | fdupes -rd /*

Mind you that fdupes is a bit slower than other tools but I found it working very nicely.