You need to tell imshow() which axes to draw the image on, unless you only have one axes.
You are updating the content of the handles structure, so you need to consider whether you need to use guidata() to update the master copy of the handles structure. Where is your code getting the handles structure from? You are not passing in the handles structure so handles.images{x} could be creating a new handles structure, but you assume that handles.listbox1 exists. Your code cannot be getting handles by way of shared variable, as shared variables only work with static workspaces and static workspaces require that there be an "end" matching the "function" line but you do not have that "end".
