Does google remove images over time? 10 points?

[Jake]

Again, after they have been removed from the site hosting the images they should eventually vanish from Google images, typically after their spider takes another look at the page, if the entire page is deleted it can take a little longer, the may assume the site is temporarily down.

One bit if research you can do

Copy the URL address of the site displaying the actual image

Do a google search for site:thePageURL (no spaces)

Roll over the result >> symbol, click Cached,
This gets you the snap shot, including the cache date, indicating when the spider last visited.
You could periodically note this to gauge the frequency of the spider visits.

The actual site webmaster could take more proactive action requesting a re-index after removing an image.