You can have a slider callback do any amount of work necessary. However, sliders are linear so you cannot use a single slider to control two different things independently: you can only use any one slider to control multiple things in synchronization. For example it would be fine to have a slider control which respective image from a number of different data sets was to be displayed.
idx = 1 + floor(get(hObject, 'Value'));
image(handles.axes7, image7set{idx});
image(handles.axes8, image8set{idx});
If you are doing a lot of this, then it is better to create the images ahead of time and update their CDATA:
idx = 1 + floor(get(hObject, 'Value'));
set(handles.image7, 'CData', image7set{idx});
set(handles.image8, 'CData', image8set{idx});
