Your problem is that it isn't in DataCad either. You just get to look at the picture through DataCad.
The first thing you need top do is to determine if it reallly is necessary to include the picture, and leave it out if possible.
When you export as DWG, the picture doesn't get included but the polyline it occupies does. I believe the AutoCad user can re-insert the picture. You have to send the picture along with all the other stuff and advise the AutoCad user what to do.
Note that so long as the picture is in the same folder as the .AEC at both ends, there is no problem sending pictures with DataCad files.
Nick Pyner
Dee Why Beach NSW