Could you have an eraser with a rectangle or square form. It will make it much easier to erase objects.
We are working on producing some variations on the 'scribble out' image which will help in this way.
Another way of making an image disappear is to morph it to another image that is off of the visible canvas with a zero animation time
First add the image and set the camera position
Then copy and paste the image, zoom out a bit on the canvas and move the second image up the canvas
Then change the properties of the second image to morph from the first image with 0 animation time
Because the camera setting is the same for both images the second image and the morph will not be visible and the image will just disappear from the canvas.