The Mac that was stolen was connected to iCloud? Did it have photo stream enabled?
Hindsight is 20/20 obviously, but ALWAYS have a backup of your data, either externally or through the cloud. Dropbox has great functionality for this and offers to set it up when you connect your photo taking device.
If you didn't have photostream on that Mac or a backup, I don't know of any options for recovering your photos except to recover the stolen computer. (Which isn't impossible either if Find My Mac is enabled on it)
It would be a good idea to eiether delete your old Apple ID or to change your login credentials so the thief won't have access to your credit card information.