Inside Mame I hit Shift+F12 to record an in-game video. Then I open the video file in a free program called Virtualdub. Once you find areas of the video where the characters are not standing then just keep copy/pasting those areas into your paint program until you get the whole stage. It can take a while to use this method, but gains you access to hard to rip games. There is a really terrible tutorial on my channel for this method.