~NES Mosaic Builder~

This works by taking the 8KB graphics rom from Super Mario Bros and splitting your original input image up into small 8x8px chunks (as NES tiles are also 8x8px). It then converts these chunks to 4 colours only. Once this is done, each individual 8x8px chunk from the input's pixels is compared against ALL the tiles from the ROM file using math. The one with the smallest difference is the "best fit" and is drawn onto the output image. It then samples colour from the original input and applies it so your output image looks good.

Sorry if this explanation sucks — I'm not too good at writing :P

Basically it can ONLY use what's in this photo to make your image