I resized a bunch of photos this week for syncing to an iPad that had limited storage. When I synced them it was obvious I lost the date stamps. Luckily I found this gem of a utility that can recursively go down all your directories and fix the date and time stamps to match the EXIF data. I was shocked how fast it was. It does a bunch of other options also, so it’s worth reading the usage page.
For my needs this is the command line I used: jhead –ft **\*.jpg
FYI it won't update any date stamp prior to 1970. It's coded using Unix standards. Unix only allows date stamps >=1970.
Download jhead here: