I am using scanline effects in MAME to simulate the old CRT look of 1980’s Arcade Machines. There are several good overlays included with MAME in the [Artwork] folder. Just add the command line switch to your front end config.
mame <game> –effect aperture1x2rb (for low res displays)
mame <game> -effect aperture2x4rb (for high res displays)
I am using RGB_KB.PNG, (attached with a few others I found.) Just detach these into your /mame/artwork folder and add -effect rgb_kb.png to the MAME command line. I don’t know who to credit for these, I found them a few years ago and Google isn’t much help. Contact me if you know and I will add proper attribution.