If you have a reference photo (one that's your own or you have permission to use!) that might make a nice painting with a few changes, using a photo editing program is a way to get an idea of what the final painting would look like. You don't have to be an Photoshop expert to do it either. A little knowledge of a basic photo editing program will get you the results you're after. Again, you're not creating a photo to put on your wall, just trying out an idea.
I use Photoshop Elements to manipulate my reference photos, though there are plenty of other programs that do similar things. About's Graphics Software Guide has a list of free photo editors and details of trial download of Photoshop.
To move the large tree to the right (as shown above), I opened the original photo in Photoshop Elements, then used the magic wand tool to select the tree (it automatically selects similar colors in an area). I moved the tree to where I wanted it to be and pulled it slightly taller.
This left a white hole where the tree had been, so I switched to the paint brush tool and blocked in some colors. I used the automatic color selector tool to get appropriate colors on the brush (basically you click on the color you want in the photo and it gets selected).
Once the hole was colored in, I used the magic wand to select some smaller trees, then cut and pasted them to the left of the repositioned big tree. Lastly I recropped the photo to remove some of the foreground in the left-hand corner which I felt dominated a bit.
Time spent: about five minutes.
