MacOSaiX is a very nice image editing application to create your own mosaics. It allows you to automatically create mosaics from images. They can be automatically discovered from the following types of sources:

Local folders

Image randomly generated from the fonts on your computer

Google Image Search

Yahoo's flickr photo-sharing service

iPhoto albums or keywords

Quick Time movies

It's as easy as a, b, c:

Choose the image you want to make a mosaic from.

Choose the shape and number of tiles in the mosaic.

Choose the sources of images to use for the tiles.

mosaic examples

Requirements
Mac OS X 10.2.8 or later.