This is a picture of me and my sister. The intent was to have two things happening concurrently – a user-controlled revealing of the image as well as a continual obscuring. I elected to achieve the former with a rectangle at the mouse, which can be used to reveal portions of the image. I tried many things for the latter effect, but all of them are based on elliptical pixel objects that pull color along their paths. Below is the code for the effect that can be observed in the first image in the post, which has a kind of echo effect that I like.

sketch249.js code