Seamless Texture in Photoshop
Make an image tile without visible seams
Also known as: Photoshop make seamless · Photoshop offset filter · Photoshop tileable texture · Photoshop pattern preview · Photoshop seamless pattern
Quick answer
To make a texture seamless in Photoshop, use Filter > Other > Offset with half the image size and Wrap Around. The edges now meet in the middle of the image, where you can fix the visible seams with the Clone Stamp or Healing Brush. Offset again to check that no seams remain, and use View > Pattern Preview to see the image tiling.
How to fix it
Start with an even, evenly lit image with no strong light gradient, remove unique marks that will repeat obviously, and keep the image a power-of-two size such as 1024 or 2048. After fixing seams, offset in a different direction to check them, and look at the tiling on a 3 by 3 grid. For PBR materials, build height, normal and roughness from the tileable color map or create the material in Substance Designer.