I'm trying to replicate an old stained paper look in my 2D game. Best way to achieve this?

It's just a simple 2D game with sprites. I'm currently adding the stains to the background sprite and then doing the same to each individual sprite. As you can imagine this can get tedious, plus I don't like the way it looks too much. I'm sure there's a way to do it on the camera itself, kind of like how cuphead has an old tv effect going on. This would also allow me to just use the skybox as the background rather than a plane sprite. Just looking for some advice on which road to take. I'm currently planning to place a png with some transparency in between the camera and the scene to overlay the effect over the sprites, but if you know a better way I'd love to hear it. I'm using the regular built in renderer, not the URP or HDRP renderers. I'm also using the 3D tools (physics and rigidbodies) instead of the 2D tools if that matters. I can switch to URP or HDRP if needed, this is an old project that predates those two which is why I'm just sticking to what I know. Thanks for any help

 

A mock up would be great, it's hard to visualize.

 

I think you'll get better visual results by multiplying the paper texture over the frame instead of using straight-up transparency, In my current game, I made a shader to blend between the paper texture and the main texture and another version of the shader to multiply them. I tend to use the multiply every time.

I recommend adding a slider too, so that you can adjust the influence of each texture.