Complete the grid with images so that each column, row, and smaller 3x3 grid contains all 9 images from the image key.
To change the image you're using, click on it in the image key to the left. To see the original picture on flickr, click on the * symbol next to it's title.
You can change the pictures that the puzzle uses using the controls at the bottom of the puzzle. You can create a puzzle using pictures from a particular user's photo stream, or from pictures with particular tags, or a combination of both.
If you want to search for more than one tag, seperate each tag with a comma. Flickr Sudoku will find pictures that match all those tags. For example, if you typed "fish, red" in the tags field, you'd get all the pictures that had both the "fish" and "red" tags.
If you're finding it hard to work with the pictures you've got because some of them are too similar, try hitting the "just get new pictures" button. This will refresh the key with 9 new random pictures from the stream or tag you selected, without destroying your work.
There are lots of different puzzles to solve, in varying levels of difficulty.
If you want to save your work so that you can come back to it later, hit the "save my game" button. This will present you with a link you can bookmark which will return you to exactly the same puzzle at a later time.