Use the alt tag to accurately describe the each image, and include descriptive content around each image. At the very least, images should contain alt tags with one or two keywords describing that image, and you should try surrounding that image with relevant text. If the image is not used in context (i.e. it is not part of a content page or an article), you should add a couple of lines below the image describing it. In essence, what you would do if you were caring for people whose browsers disabled images and those who wanted some details about the images.