You can solve any sudoku puzzle generated here without making notes, and they all have only one solution.
If you try to place a picture where it already exists on that row, column, or small square, both occurrences will be highlighted in red. If your mistake is more subtle, you can click the 'give me a hint' button and any errors will be highlighted in red, or if you've made no mistakes, a green square will show where you can go next.
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