Funny Mask is a fun application which tries to detect faces on the screen, then customises them with clipart-type masks (hats, glasses, wigs, more).
To use the program, launch it and click "Draw On Screen". Funny Mask uses OpenCV (the Open Source Computer Vision Library) to look for faces, and adds one of twelve silly customisations to anything it finds.
By default the program chooses a mask at random. If you have a preference, click the arrow to the right of "Draw On Screen" and select that option from the list.
If you want to save the results then of course you could press PrtSc, and paste the image into a graphics program. But it might be easier to just press Capture, which grabs the full screen and saves it as FunnyMask.png in the Funny Mask folder. (Unfortunately it always uses this file name, so clicking Capture again will overwrite the previous image.)
Funny Mask didn't always work for us. It had problems recognising faces which were cropped too tightly, for instance. And if a face is tilted then the mask won't always be in the right place.
The program got it right enough times to be worth trying, though. It's fun and easy to use, great as a way for kids to mess around on the PC. And there's a bonus extra for the more experienced: the bundled 12 masks are just PNGs with a transparent background, so it's easy to customise them or create more.