In Builder, the easiest way to do this is to create specific stimuli that correspond to the clickable region of your main image stimulus. For example, you could create a polygon stimulus (like a rectangle, or with say 99 sides, effectively a circle) and overlay it upon your background image, one for each clickable region. Initially, give the polygons a colour so you can see if they overlap correctly, but when you know they are in place, you can set them to be invisible.
Then you put the names of those clickable polygons in the “clickable stimuli” field of a mouse component. Then you can specify that the routine ends on a “valid click” (i.e. one that falls within one of the clickable stimuli). That name of the clicked stimulus will be recorded in the data. If you need more info recorded, you can add the attribute names (like pos) to the field 'Store params for clicked".