Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
Background pattern originally a PNG drawn in Paint.net
Source Firkin
Prismatic Curved Diamond Pattern 4 No Background
Source GDJ
A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.
Source V. Hartikainen
Clean and crisp lines all over the place. Wrap it up with this one.
Source Dax Kieran
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Retro Circles Background 4 No Black
Source GDJ
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Little x’es, noise and all the stuff you like. Dark like a Monday, with a hint of blue.
Source Tom McArdle
Prismatic Curved Diamond Pattern 4 No Background
Source GDJ
From a drawing in 'Bond Slaves. The story of a struggle.', Isabella Varley, 1893.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
A repeating gloomy background image. This one consists of a pattern of black chains layered on top of a dark textured background.
Source V. Hartikainen
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Lovely pattern with splattered vintage speckles.
Source David Pomfret
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
An alternative colour scheme to the original seamless pattern.
Source Firkin
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
A background pattern with green vertical stripes. A new striped background pattern. This time a green one.
Source V. Hartikainen