One important step to help improve search engine optimisation is to make sure all your images have image alt tags. There are 2 alternate tags, one called title tag(used by old browsers such as Internet Explorer), the other is called an alt tag. These are not only good for SEO, but if visually impaired visitors visit your site, they may be using assistive technology like screen readers or other text to speech software which reads the page out loud. This software will then read the alt text.
An additional benefit is that the alt tag can provide a good description of images for search engines. In turn this can lead to more traffic through Google images and have a positive effect on SEO. It is important to keep the text short and avoid jamming the text with keywords.