So - some questions. Is this for all iMessage photos or just the ones from your son? Have you tried turning off iMessage (on the iPad, via the Settings app) and then turning it back on? Can you/have you tried a different e-mail address for your iPad's iMessage account? Have you tried closing the iMessage app fully and then doing a restart and/or a reset? If you put the iPad into safe mode, can you then see/keep the photos (trying to determine if this is a jail break problem or an iMessage problem...)?
Sometimes, iMessage is a confusing mess that I am hard pressed to understand. So, it might or might not be a result of the jail break - it could be that your iMessage is messed up. So, I'd recommend the turning it off/on step to start.
Hopefully, someone else will come along with some more ideas (or one of these questions will help/work)...
Hi Marilyn, I switched Imessage off and then on again and it's working! I could have sworn I had tried that already! Thanks, you are an absolute star!!!!!!!!
Yay! Glad to hear that things got sorted for you. And, thanks for coming back and telling us your problem got resolved. Always nice to hear back - especially the success stories.