Image search optimization (or image search engine optimization) is the process of organizing the content of a webpage to increase relevance to a specific keyword on image search engines. Like search engine optimization, the aim is to achieve a higher organic search listing and thus increasing the volume of traffic from search engines.
Image search optimization techniques can be viewed as a subset of search engine optimization techniques that focuses on gaining high ranks on image search engine results.
Unlike normal SEO process, there isn't much to do for ISO. Making high quality images accessible to search engines and providing some description about images is almost all that can be done for ISO.
Checklist For ISO
Use a meaningful name rather than 'DC00001.jpg'
Separate words with a hyphen or underscore, but try not to use too many. i.e. green-tree.jpg and green_tree.jpg are better than greentree.jpg or DC00001.jpg.
Provide a small description of image in alt attribute of img tag.
As a good practice do not leave alt attribute empty, provide at least one word.
Do not fill the alt attribute with lots of keywords, even if they are relevant.
Text Around The Image
Place some text around the image that describes it.
Try to use high resolution images.
If available, provide different resolutions of images
Make sure that the directory that contains your images is fully accessible by crawlers.