With Foto-Mosaik you can generate a virtual mosaic from any photo, using your own image collection as an enormous box of mosaic color tiles. The program takes care of everything and your intervention is limited to selecting the folder where the photo tiles should come from and the one image you want to convert into a mosaic.
The first time you run Foto-Mosaik, you need to create a tile database with your pictures. The larger it is, the better results you'll get in the long run, so be prepared to wait for quite a long time while the program creates the database.
There are several options to customize before creating the mosaic, such as the number of tiles to use or paper format (portrait or landscape). Bear in mind that you'll need a high number of tiles in order to obtain a fairy good result. Ideally these tiles should also be quite varied in color and light, otherwise the resulting mosaic will look plain and dark – or it won't even resemble the original picture at all.
With Foto-Mosaik - and as many photos as you can gather in a database - you'll be able to create a beautiful mosaic from any of your pictures.