Adding screenshots from the lectures to the course notes is a nice way to contribute. Udacity's Wiki has the capability of hosting images.
You may follow the instructions bellow and use the image uploader to upload images (diagrams or screenshots, etc):
Click the Link Below to open the image uploader:
- Image Uploader
You will also find the following text at the bottom of Wiki Editor's textbox:
You can always click the link "upload images" to open the image uploader from whatever Wiki page you're editing.
Just browse for the image you want to upload from your computer's hard-drive.
Then click "Upload". The following screen should show:
To put this image in your wiki page, just copy one of the Wiki Codes (there are three sizes available) and paste it into the position you want to insert the image.