Create a file photorec.sig in your home directory.
This photorec.sig file must contain the newline-delimited file signature/s of the file/s that you want to recover.
For example, a user wants to recover foo.bar. The header signature of foo.bar is 0x41414141.
The user must add a line -
bar 0 0x41414141
to photorec.sig where bar is the file extension, 0 is the signature offset, and 0x41414141 is the header signature.