Back in the late 80s, I learned much about computer programming from this book: Write Your Own Adventure Programs For Your Microcomputer. This is the same book that I used as a guide when creating Malfunction for my Apple IIgs back in 1988.
This afternoon I came up with a handy little bookmarklet (or favlet) that uses the site dummyimage.com to create a place holder graphic. Simply drag the following link to the button bar of your browser:
When you click the bookmark it will prompt you to input image dimensions. Use the format, WIDTHxHEIGHT (for example 640x480) and a new window should open up with a downloadable GIF with those exact dimensions.