I'm not sure if I'm correctly understanding your question; I think this will work nicely replacing the tables with image() calls, as you suggest:
$mc->qa ( "Select the graphs that define a function.", image("imagefile1.png", options) . $BR, image("imagefile2.png", options) . $BR );
and so on. I can think of some other ways to do the same thing (e.g., with pop-up options for each graph:
<http://webwork.maa.org/wiki/PopUpListsLong>), but not anything that seems strikingly better.