TLDR: Not JPGs, BMPs more likely.

I recall when the first LCD TVs came out and I wanted to get a cheap 1080 one. The problem was that almost every TV said 1080 even if it was just 720 upscaled.

I put a uniform image in BMP on a memory stick - every column being R, then G, then B repeated. As the image was exactly 1080, viewing it in full-screen on a 1080 screen gave a sort of uniform grey color. On an upscaled monitor you could see very visible banding.

This would not have worked had the image been JPG.