For my website I specify a background color and a text color for dark and for light theme, but when there is a background image I should really specify alternate image, or override the text color. For this page however you can see the effect by clicking the theme icon to to toggle between dark and light text, but without changing the background image.
To make my "framed" theme, I was inspired by a website that was still using dated Frameset technology. One of that site's features was a tiled textured background image as was fashionable in the day. It's intention is to suggest one is reading from luxury textured paper, but without transferring huge background images to cover the whole page.
As an amateur photographer I had often wondered how they make the tiles blend together so well that you don't see seams or pattern repeat. For me the best way to explore is to dive in at the deep end and see how I would tackle issues thus to get an understanding of what is involved.
Superimposing flipped images to make the edges blend is going to produce the appearance of a repeating pattern. Patterns are fine if that's what you want, but it wasn't what I was trying to do. To demonstrate the effect of large structures in the image I've done it here anyway with the above corn paper photo.
One can argue over esthetics, but a busy background pattern makes text tiring to decipher. With that said, on this page I'm delibetrately inserting gaps so the text doesn't detract too much from the background that I'm talk about.