PHP image pixelate?

Question

I need to make this effect with php. I know that there is IMG_FILTER_PIXELATE in PHP image filter. But I need it to be smoother and embossed? like in this image:

This effect will make any image uploaded by user become pixelated and the edge of the picture become red (I know IMG_FILTER_EDGEDETECT but I don't know how to use it to change edge color).

I have no idea how to do this.