The website owners must optimize their images for better search results or for their rank. Adding an alt text to images you will provide the relevant search results for your visitors.Alternative text is useful in the case when the image cannot be found. Google interpret the alt text in the same way like the hyperlinks. Because some images do not have hyperlinks Google will use the alt text for the SEO value.A thumbnail is a small representation for an image.The page will upload faster. For details see:https://en.wikipedia.org/wiki/Thumbnail