Put the images in a related table. Now you can select which image is visible by controlling which value is stored in the form's match field that links to this table of related images.
Say you have an images table with two fields Image ( container ) and ImageID (auto-entered serial number)
You can link it to your Form's table like this:
FormTable::ImageIDField = Images::ImageID
You can now place the Images::Image field on your form layout. If you put a 1 in FormTable::ImageIDFIeld, you'll see image 1. If you put a 2 in FormTable::ImageIDfield, you'll see image 2 and so forth. Note that this trick will allow you to work with any number of images should your needs change in the future.