Choosing the Proper Kind of Photo:
For this tutorial, we're going to simply transform a photograph into a stained glass Photoshop project, rather than hand making a stained glass image. This allows people that don't have a wealth of artistic ability, or those who don't have the time to go through the lengthy process of starting from scratch.
This might surprise you, but not every photo can be magically transformed into stained glass. Detailed pictures or pictures that lack any contrast whatsoever often do not easily make the leap from photograph to stained glass. That being said, some do work out very well. Ideally, you want a picture where the subject has some contrast to the background. A blockier, less detailed subject often works well, but don't think you need to limit yourself. This effect doesn't take very long to try out and can easily be tried on several photographs until you get the right fit.
Open your photo in Photoshop. Ideally, your photograph should be a decent size, because the smaller it is, the more detail will be lost. Here I'm using a cute little Sulfur Crested Cockatoo, not only for the birds recognizable shape, but also because his white and yellow stands out very well against the blue background. This will make it so when we remove the details and place the stained glass mosaic on the picture, you will still easily be able to tell what it is.