One of the reasons I like using Photoshop Elements is the range of artistic filters it has. I usually use the palette knife filter, sometimes the watercolor one, but there are a bunch of others. As you can see in the photo here, which has had a palette knife filter applied to it, it enables you to really get a feel for how the painting might turn out.
Filters are really easy to use: you simply select the one you want and let it do its thing. There are various parameters you can adjust in each filter, e.g. to get more or less detail in the painting (as if it were done using a larger or small brush or palette knife). A preview shows you what the effect of the adjustments are.
If I'm happy with the outcome of an altered reference photo, I'll print it out and use it when I'm painting. Sometimes I'll also use the original photo, sometimes not. Usually, at some stage during the painting it takes on a life of its own and the reference photos are put aside.
If you haven't got your own photos to use for paintings, here are some places to source reference photos.
