Mathematica's symbolic representation of both graphics and controls makes it particularly easy to create click-interactive panels in which the user clicks or drags elements embedded in a fixed overall image.
Dynamic — set up dynamic variables and a dynamic overall display
DynamicModule — localize and save dynamic variables
LocatorPane — place one or more locators with arbitrary appearances on any image
LocatorAutoCreate — option to allow new locators to be created by clicking
Locator — set up a movable thumb connected to a dynamic variable
ClickPane — respond to the locations of clicks on any image, perhaps dynamic
PlotRange — specify a fixed coordinate system