Here are some additional tips and tricks I have learned from this technique.
-Tissue, as most of us know, is very thin and can be seen through. Even artist's tissue is not completely opaque, although it is a bit thicker. This means the white of your canvas can be seen through the paper, so if you want to avoid your photo looking washed out, raise the Saturation of the colors and lower the Value or Brightness a little before printing.
-Another artistic approach is to paint the canvas in one solid color or a gradient. This will create a soft undertone for the whole picture.
-Do not use too much sealant! One or two even, light layers is plenty. To do this, hold the can of sealant or fixative about 7 inches away from the picture and then spray over the whole thing using slow and steady movements. It's best to do this outside.
-This method of printing on tissue and adding it to canvas works well for other surfaces, too. Tile and wood are two I have had great success with, but it can also be used to make personalized greeting cards and scrapbooks as well as a lot more I have not even thought of yet.