Step 1:

-steal a Whovian’s laptop (momentarily)

Step 2:

-create a folder in iphoto full of multiple images of their current desktop background

Step 3:

-place one picture of a weeping angel amongst the many images of their current desktop

Step 4:

-set that folder to be their desktop background, changing the photo every so often

Step 5:

-put laptop back, laugh villainously, and listen for a scream