What kind of volume were those files on – NTFS, FAT32, other ?
You can try Photorec, which will “carve” every file it identifies based on its signature, with no regard to the filesystem's records which can be obsolete (in “File options” you can select which specific signatures you want it to search : for instance you can ask it to target JPG files only, if that's what you're looking for). It can get false-positives for certain file types, tough, even with JPG pictures the detection is not perfectly reliable (after all that's what the program was designed for originally, hence the name), but if it doesn't
find the files you're looking for then you can be pretty confident (or dismayed) that they can't be recovered.
Recuva (in list display mode) tells you if a file which has been detected based on the volume's filesystem has been partially or totally overwritten, and by what other file – although it is not always reliable.
With R-Studio, you can right-click on any file in the recovery tree and select “View/edit” to open the hexadecimal viewer : if you don't see a valid header (for instance a JPG file always begins with “ÿØÿ”, or FF D8 FF), then at least the first sector has been overwritten. If the first sector has been overwritten, then it's virtually impossible to recover the file even partially (besides, if the first sector is overwritten there's a good chance that the rest is as well, as JPG files are quite small).
For further investigations : in the bottom left corner of the hex viewer, select the “properties” tab, then note the value given at the bottom in front of “Sector” (that's the first sector number). Then there are several methods I know of to determine what file currently occupies that sector :
– R-Studio using the “show files in hex editor” feature (but it's quite complicated)
– nfi.exe (command line tool)
– Defraggler (Piriform's defragmentation tool, which can provide a list of files occupying a given “block” – but so far it does not allow to directly input a sector number, I recently requested such a feature, which should be easy to implement)
(I provided detailed explanations here
Then with WinHex uou can open the recovered file (R) and the currently allocated file (A), search for a specific enough string from the begining of R inside A, then synchronize both windows and scroll down to verify how much of A is actually now part of what used to be R... and so on...