What are 'dup0' files in the photos folder? Today when I wanted to copy some photos and videos from my Samsung Galaxy S to my PC, I noticed that inside the photos folder (DCIM\Camera) there are a lot of files with the extension dup0. They have the same filename as the photos/movies (e.g. img1.jpg and img1.dup0), but not for every photo a dup0 file exists.

What are these files for? Can they be deleted to free some space?

Update / additional information: the dup0 files are quite small for photos (e.g. photos are about 1.5 MB, dup0 files about 50 kB), but for movies, they can be quite large (e.g. 16 MB for an 18 MB movie).
Rename the file with the appropriate extension and find out(ie rename img1.dup0 to img1-1.jpg and open it). In the case of the image files I think they are the corresponding thumbnails since the size is small