hmm...
I don't know, since I have tried to manipulate images in a report, and CR doesn't provide any methods to interrogate the image so that one can change the size....but if the application knows the size, I guess you should be able to manipulate the size of an object.
I think that in general you would need to name each object and I think that you can manipulate objects if you know the names, but again, I haven't ever done this. I usually just manipulate the data, pass it to the report and then have the report respond to the data.