Making an image look like its on a canvas?

I use either the Texturizer filter or a Pattern Overlay.  You can add different texture images in both cases to increase the number that are there at the start.  You will want to change the Blending Mode. The Pattern Stamp tool allows you to load a number of Photoshop artist surfaces including canvasses, which can be used as a Pattern Overlay.  There are many different kids of canvas in real life and the Pattern Stamp feature contains a few of them.

David

You could take one good picture of your canvas en reuse it.

Place it as a layer on top of the image and try out some belending styles, like Multiply. You can lower the opacity of the layer if desired.

Make sure to make the canvas-layer a Smart object so you can resize is with less quality loss.

Hello! To fake canvas in Photoshop, try Filter>Texture>Texturizer, and select canvas or burlap as texture.

Artistic>Underpainting is an alternative. (or you could combine them)

'Transform' can skew rectangular shapes to have perspective. Here's a loosely related tutorial or two...

http://www.tutorial9.net/tutorials/photoshop-tutorials/designing-a-software-box/

http://psd.tutsplus.com/tutorials/tools-tips/create-a-3d-software-box-in-photoshop-using-actions/

You can have your image printed on canvas stock and buy canvas stock for many inkjet printers.  If your asking how does one add a fake canvas texture to an image Photoshop has a filter that support 8bit documents that can add a canvas texture to a layer.