You may need to click each image to see the images in a larger scale to truly see the effect, since WordPress tends to shrink images to fit.
For scanlines/shaders, you’ve gotta go into RetroPie Setup. From there, Configuration/Tools -> Config Edit -> Config Basic libretro emulator options. Now here you can choose to apply the shader to ALL of the emulators (option 0) or do it for individual emulators. I’m using Final Burn Alpha, so I went to Configure additional options for fba. Option 3 is Video shader enable (3). Click that and enable “True.” Next is Video shader file (4). I chose crt/crt-hyllian.glslp . You can choose it with the glow (crt/crt-hyllian-glow.glslp) to add that aged CRT look. I think there are others that will mimic a curved monitor’s surface. Tinker around and see what you like.