Number five from the same submitter, makes my job easy.
Source Dima Shiper
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Prismatic Floral Background No Black
Source GDJ
You know you love wood patterns, so here’s one more.
Source Richard Tabor
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
Sometimes you just need the simplest thing.
Source Fabricio
Prismatic Groovy Concentric Background No Black
Source GDJ
This is indeed a bit strange, but here’s to the crazy ones!
Source Christopher Buecheler
The image is a seamless pattern which is derived from a vine .Consequently, the vine got like dots via vectorization.The original vine is here:jp.pinterest.com/pin/500744052301410188/
Source Yamachem
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Inspired by a JPG that was uploaded to Pixabay by kokon_art
Source Firkin
This is a semi-dark pattern, sort of linen-y.
Source Sagive SEO
From a drawing in 'An Old Maid's Love. A Dutch tale told in English', Maarten Maartens, 1891.
Source Firkin
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib