I uploaded an image, it was 1920x1080, and it looked like something from 2012. It looked so buggy and pixely, I just want to know what the resolution of a scratch project is. I don't want this problem effecting all of my projects.

480x360.
However, you can upload an image at 960x720 and it will not be as compressed.

The Scratch stage is 480 pixels wide by 360 pixels tall. If you don't want your images to look like they came from the Late Cretaceous, head over to this shameless promotion.