I tried submitting my Battle Garegga score to this site with screenshots (I forgot to record myself playing it), but some people weren't convinced (including one person who voted that I stole the pictures).
Is there a way to improve the screenshots? My only guess is to have a "real life" screenshot -- a picture of my monitor with the game running with my tag on the side.
But I seriously don't want to play it again cause I'll probably get a worse score than before, but I think I have no other choice...
Yes, definitely use those. Also, if you video record for MAME, it's good to show that the settings are set at default real quick (just to show the number of lives weren't tampered with or anything), then switch back to the game.