Mosaickr is an online tool that allows you to create your own mosaic using photos from Flickr. You can create your mosaic from your own photos or search by tag through others photos (with a creative commons attribution license) and add those. To create your mosaic you have to first select a main photo, and then whether you want to make a small, medium, or large sized mosaic. Your mosaic size choice determines how many additional photos you need to select. A small mosaic requires between 1 and 3 hundred while a large mosaic requires somewhere between 3 and 5 hundred.
If you're really particular with your mosaic you can select all 500 tiles individually, the rest of us can import photos random by tag 50 or 100 at a time. You final masterpiece take a bit of time to make, but can be emailed to you. A low-res version is free, and a high resolution image will run you 1.49 Euros. If your mosaic truly is a masterpiece there's also a poster option available if you're in one of the supported countries.
