Turn sudoku string to PNG image

Hello, I need a PHP function that receives a string of numbers and outputs a Sudoku puzzle PNG image. Example: 093002070700100092100407500080500306010023040407600020009301007870006009040700250 Will output a PNG image as attached. So if the php file would be called [login to view URL], I want to be able to make this call in the browser [login to view URL] And this will output a PNG image of the Sudoku The size of the image should be exactly 320px X 320px. Image design should according Sudoku design (3x3 region is in bolder border) Numbers are from 0-9. Each number represents a cell. 0 represents an empty cell with a white background. 1-9 represents a cell with a number with a gray background. The first 9 numbers represent the first top Sudoku row from left to right. The second 9 numbers, represents the second row from the top (from left to right) and so on. The main concern here is complexity and system resources usage the function takes. I need it to stay as much "low cost" system resources usage, as it can. So I was thinking that instead of generating each cell, every time, maybe to create all the images possible upfront, and just "add" them to the bigger puzzle picture when the time comes. There should only be 10 pictures/cells 1-9 with gray background, and an empty cell with white background. Please include as much comments as possible.