I had to use ChatGPT and a huge amount of debugging, but eventually figured it out.

It is a very niche problem with a very strange solution, where I had to copy the image I got from the webcam onto a new image, resize it, copy the resized image and then give it to the pixelate function.

The problem was something to do with the way my function was creating the face image and didnt actually have anything to do with the size of the image since even when the faceImg was bigger than my test image it still would not work, but copying and resizing and copying again did the trick.

I have no idea how this fixed it but maybe someone smarter than me would know some kind of bug or something that would cause this