When you assign useful names to images on your website, then the search engines can use that name for its image search. So, when somebody searches for the name of your image, then it is likely going to show up in the image search results. That said, you should include keywords in your image name and not something like hughr1932938. You should also include the correct alt tags. The alt tags are for saying what it is a picture of if the viewer is browsing the web with images off, or a search engine wants to index the picture. Remember, the search engine crawler cannot view graphics. Also be sure to check out Google’s image publishing guidelines.