They are 960x536 JPEGs with an extra 292 bytes added the the beginning of the file (header information used by the game and RGSC). They can be converted to normal JPEGs by removing the first 292 bytes with a hex editor and adding .jpg to the file name. Photoshop, IrfanView, and some other image programs (but not all) can detect them as JPEGs and open them.
Any info on the format used for them pics i.e. if they're a modified PNG/TGA/JPEG or something like that?
No, not quite. The actual file structure is like this:
int32 magicNumber //0x01000000
byte //Unicode string in the form "PHOTO - date time" with padding
char imageMarker //"JPEG"
int32 imageSizebyte[imageSize] //actual JPEG image
byte[bufferSize - imageSize] //random leftover data from the gfx buffer
char jsonMarker //"JSON"
char[jsonLength] //image metadata
char titleMarker //"TITL"
int32 titleLength //usualy 256
byte[titleLength] //title is actually a null-terminated string, but the rest is random filler-data
char descriptionMarker //"DESC"
int32 descriptionLength //usualy 256
byte[descriptionLength] //again null-terminated with random padding
char end //"JEND"
So it's not enough to remove just the first 292 bytes, you have to remove the end as well, relative to the JPEG size.