If you haven't created an account on Picnik, do that first. Picnik is free and all they require is a username, password and your email address. You may also want to consider upgrading to Picnik Premium to take advantage of even more photo editing features.

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Before you go to the template to print photo onto canvas, edit your image in Picnik's free editing program. First, upload your photo by selecting the option from the Home tab when you log in. The picture should upload within a few seconds, after which you'll be taken to an editing page. At this page, you can
crop the photo, sharpen it and remove red eye.
To do more with your photos, click on the Create tab and you'll get another set of options. One great effect for canvas photos is the vignette feature. This puts a gentle dark border around the edge of your photo. The matte effect, which puts a lighter border around the photo, also looks great on canvas. Both effects can be seen below.

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click to enlarge