If you made some photos with a camera having a wrong date/time, the corresponding exif metadata are wrong for each photos. Then, you can use the jhead software to adjust dates of these photos.
This command will subtract 11 hours and 40 minutes to each jpg files in the current directory:
jhead -ta-11:40 *.[jJ][pP][gG]
If you want to add 2 hours and 15 minutes:
jhead -ta+02:15 *.[jJ][pP][gG]
Of course the jhead tool can do a lot more: just type man jhead and read !
For example, you can rename all your photo filenames from there dates:
jhead -n%Y%m%d-%Hh%M-%04i *.[jJ][pP][gG]
Discussion