exiftool is a very useful utility that allows you to query or edit EXIF information from pictures. Going through some of my pictures recently, I have found some sets of pictures with incorrect date in the EXIF info, be it a few hours off or even 1 year and a few days off. Fixing them one by one was not an option, so after a couple of searches on google I found exiftool. It is a command line utility that lets you edit EXIF information and you can do it in batches of files or folders, even using conditions to specify when a change must be applied.
For me, the need was only to change some photos info so that it shows the real time they were taken, three hours before the saved setting. The command was as simple as this:
exiftool -DateTimeOriginal-='0:0:0 3:0:0' -CreateDate-='0:0:0 3:0:0' myfolder/
The format for date changes is ‘YYY:MM:dd hh:mm:ss’.