Whenever possible, images should come from the public domain or Creative Commons.
All images and media should be accompanied by attributions. The attribution should be directly beneath the image, in the caption field, or located in the lower right box on the page.
All images and media should be accompanied by alt text descriptions.
Alt(ernative) Text can be provided to give additional information about an image or graphic. Sometimes this text displays when mousing over the image. It is especially important for accessibility puproses, as it gives a screen reader a description to read in place of the image. If this text is not provided, the screen reader will simply say "image" or read the file name.
Alt Text should be concise and clearly explain what the image is. In most situations, it is also helpful for Alt Text to give insight as to why the image is significant or why it was included. Many websites refer to this as capturing both the content and function of the image.
You do NOT need to use phrases such as "image of...." or "graphic of...."
When you have the Image Properties (editing) window up, there is an Alterative Text field.