I can think of a few ways. One would be to set the container with a script trigger. The attached script would go to field if empty or else load a new popup window of a new layout with the same container enlarged to near full screen. Set the feild to enlarge to fit ...
Alternatively, you could save a reference to the image and use "go to field by name" button beside the file reference. Make sure you turn on "select/perform" of the container field. When you click the button it would activate the file attached which could then open the PDF of the image )or whatever the file format)
I use an additional layout as a popup, set the image container with a button script, they click it and the layout pops up with the larger photo version. If you have several images for each record you can even setup NEXT, PREVIOUS arrows to browse the images at full size and a CLOSE on each window.