Image composition let you create a composition of images of different aspects and dimensions, then scaling them to fit into a single rectangular block on the page.
It's a wrapper around the the "magazine layout" algorithm described by Harvey Kane http://www.alistapart.com/articles/magazinelayout/
2014-06 deprecated in favor of Imagematrix, or collageformatter.
This allows you to add multiple images to a single node and then choose to display all of them together nicely when viewing the node.
If you want a view renderer that will do the same thing for the results of views then please see Imagematrix. It does the same thing, in the same way, using a copy of the same code, but works on compositing view results. This module works on multiple image fields attached to single nodes.