The IMAGE_DATA items relate to atomic RADII sizes and Connolly surface generation.
The IMAGE_DATA menu block is loaded with the file MAIN_CMDS:load_image_data.com.
Sets radii of "display" atoms to VdW radii, whatever their values in MAIN are.
You can check them with command
> show radi sele display end
Multiplies the radii of "display" atoms with 0.5. Clicking it twice you get a quarter.
Enables you to radii of "display" atoms to your value of your choice (MAIN_CMDS:image_data_rad.cmds).
Generates Connolly surface with the default density of 5 points per sqare A (MAIN_CMDS:image_gen_poin_surf.cmds).