It worked !
Thanks a lot for helping me and for PM me, I had given up thinking GntlmnBndt's intervention had killed it in the egg (I can understand though...bad timing for me).
I still wonder why so few people encounter this problem, I have it on several different PDF and I spent like 3 hours querying google without any result ("images don't display ipad pdf", ...). It is the first time I hear about the jpeg2000 format. I feel I'm just getting old...
Well I guess the next me will find this thread & solution faster
ps : Btw great forum for ipad readers...I'll lurk here for a while :-)