Mazaika is a photo mosaic tool. It can create pictures made of other pictures.

How Mazaika works:
Every region of the source image is replaced with some image from a collection, that most closely resembles the original image. When searching for an appropriate image Mazaika considers not only the overall color of the source image part but also takes into account the inner color and the brightness distribution within.
The more pictures in your collection - the more accurate the match. The more different colors and brightnesses in the pictures in the collection - the more accurate the match. In the gallery section you can see some source pictures rendered with different collections.
 

There is a dog photo rendered three times with three collections. The one from the collection of 5000 animal photos seems best. It is very subjective, but the dog made from a collection of 2000 beer bottle labels seems good too. The third dog - made from a collection of 7000 windows icons (bigger than two above) - seems slightly weak and dull. Nevertheless, the face of pin-up girl made of small a collection of 1700 windows icons is very pleasant.
It appears that not every image can be rendered with every collection. Good results can be reached even with collections of under 1000 pictures. You can see the samples in gallery 2.
Obviously the more cells (tiles) in source the picture - the more detailed the mosaic will be. 1000 - 2000 tiles is usually enough. My experiments with less than 1000 tiles can be viewed in gallery 2
Mazaika can consider small parts of the tile pictures to make up detailed parts of the larger picture. This means that two or more tiles may work together to correctly represent a section of the big picture.
Mazaika is the only photo mosaic program that allows you manualy change single tiles if you don't like them.
See large, highly detailed pictures in gallerys.
 

Mazaika v 3.1 Features
Real time color correction and blending in the main screen.
Option to Correct Tile Colors.
Option to Sharpen Tiles in mosaic.
Allows you to save a really huge files up to 10Gb and more.
Context help system.
Wizard type interface.
Zoom in/out view of the mosaic.
Right click popup to show candidates for current cell.
Right click popup menu to view original tile image.
Smart rendering mode to fill key image areas first.
Manual rendering mode to change single tiles if you don't like them.
Repetition tiles count control.
Tile resampling for best output quality.
Optional blend tiles with original image.
Custom cropping adjustments for tile library.