Last time I evaluated this, sixel & base64 image placement relative to re-positioned cursor had slightly different behaviors across different implementations. I think the only one with well-defined placement/dimensions behavior was the Kitty format--which is unfortunately Kitty-only.

https://sw.kovidgoyal.net/kitty/graphics-protocol/

If the goal is to hot-patch graphics into existing TUIs, Kovid is probably on the right track with this. It needs to be something richer than what sixel or iTerm2 provide--with pixel placement, play/pause, scaling, etc. Though for a do-over of piping a UI over a (relatively) low-bandwidth wire, I think something like Sun NeWS would have been a simpler & more feature-complete approach.