Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Here's a subtle marble-like background for use on websites.
Source V. Hartikainen
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
Number 3 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Zero CC bark from fur tree tileable texture, photographed and made by me. CC0
Source Sojan Janso
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Black brick wall pattern. Brick your site up!
Source Alex Parker
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Small dots with minor circles spread across to form a nice mosaic.
Source John Burks
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
ZeroCC tileable mossy (lichen) stone texture, edited from pixabay. CC0
Source Sojan Janso
This seamless light brown background texture resembles a wallpaper with vertical stripes. One way to use it is as a tiled background on web sites.
Source V. Hartikainen
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley