Joyfulltou
Annoying isn't it.
There are a few things you can do, none of them ideal but maybe of help to
you.
Use an AutoShape as the frame for your picture. Use Fill Effects in the Fill
tool and choose picture. Once animated you can change the picture without
the
animation being changed. Could be you will have to play with the
measurements or shape of you rAutoShape to get a good result.
Second thing: apply your animation to "Object Area for AutoLayouts" in the
Slide Master
When you create a new slide choose a layout with content placeholders.
Insert picture into the slide by clicking on the "Insert Picture" or "Insert
Clip Art" button.
Now when you delete such a picture you are left with an empty content
placeholder.
Put a new picture in the placeholder it should keep it's animation.
Luc