Right clicking on the image container and clicking conditional formatting. Then clicking add and changing the condition from value is to formula is. Set up a formula so when the container is empty it will blend in with the background. You will have to pick the colors though. Does that help?
Or use a related table for your pictures with one picture in each related record. You can then set up a portal with a scroll bar to display your pictures.
It's also possible to set up duplicate layouts by selecting this option from the layout menu while in layout mode. You can then modify the copy of the layout to have additional container fields and use the OnRecordLoad trigger to perform a script that changes layouts to switch to the correct layout for that record.