Before uploading an image to the web, first change its filename to a word or words that make sense, rather than a label such as bannerimage13.

One reason to do this is that the filename is the default for the image’s title text in WordPress, so when the user hovers over the image with her mouse, the text (e.g. bannerimage13) appears. The second reason is that the filename becomes part of the URL for the image, and it’s better for search engine optimization to have a real word that might be part of a search term.

This brief extra step is well worth the time it takes.