you know... thinking about it, maybe auto hot keys could be configured to do something like this? it has graphical overlay functionality and you can configure the opacity for the overlay.
and that website really needs a dvorak preset for the buttons!
UPDATE:
here's some auto hot keys code i was screwing about with for a semi-transparent overlay, the opacity level is controlled with the winset line - 0-255 I believe. Adjust width/height to measure, and of course change the triggering response - here's it's ctrl+shift+f5 - you'd want to accept some kind of input for which image to show.
also, not sure how to close the overlay!
^+f5::
#Persistent
#SingleInstance, Force
Gui, Add, Picture, x0 y0 w400 h400, C:\path\to\image.png
; Removes the Border and Task bar icon
Gui, +ToolWindow -Caption ;+AlwaysOnTop
Gui, Show, W400 H400, Test
WinSet, Transparent, 180, Test
Return