After you save your picture, go to Photoshop. GO to File > Open. Go to the directory your picture is in, and open it. Alternatively, I believe you can right-click on a picture on the internet, select "copy." Go to photoshop, and select "new." I believe Photoshop should adjust dimensions for pictures on the clipboard, therefore, you can select "ok."
[EDIT] A good website for learning some cool techniques is
www.good-tutorials.com.