Here you can find information about Morrowind Screenshots project.
file format
Screenshots should be initially captured and drawings saved in "PNG" graphic format (uncompressed), minimum dimension is 800x800, maximum file size is 5 MB. For videos "MP4" or "AVI" format with a high bitrate is suitable, maximum dimension is 1080x1080, minimum duration is 10 seconds, minimum framerate is 30 fps, maximum file size is 200 MB. Files can be folded into a "ZIP" archive for easy transfer, maximum file size is 100 MB.