As I read Lawrence's McBride's post Is It "Snowing" Outside Your Listings?, it occurred to me that using Photoshop's lasso tools to select the outline of a window is a very useful real estate photoshop skill, and because windows are mostly of a uniform, regular shape without complex, curvy lines (no matter how ugly they are) they are excellent objects on which to practice your lassoing skills.
First find a photo of an ugly window. Here's one from my reject file. You can even right click- and Save As - for your own use, completely free of charge!
Click the lower right corner of the Lasso Tool , and choose Polygonal Lasso.
Click in the upper left corner of the window, to anchor the Lasso, drag along the top of the window, as you drag, a wobbly line will form, click in the left corner to anchor that point, and the line will straighten out.
Drag down the right side of the window, as you drag, you'll get a sense of how the line moves. When you reach the lower right corner, click again to anchor.
Drag along the bottom of the window, click to anchor in the lower left corner.
Now drag up the left side, and when you reach your starting point in the upper corner corner, click again to connect. The Lasso line will turn into the familar "marching ants" indicating a finished "selection".
Now you can made edits to just that selected area without changing the rest of the image.