An image alt tag is the text that appears in a small box when you hover your cursor over an image. Alt tags should convey the key information from the image that the user would not receive if she had image loading turned off or she was visually impaired. Search engines also look at alt tags to a limited degree, so it’s helpful if the alt tag contains relevant keywords. Not all images have or should have alt tags defined. For example, graphical borders should not, as that would make for a very frustrating user experience for a blind person using a screen reader.