When you are building a website that makes use of a lot of images, you probably want Google to index the full-resolution images rather than just the thumbnails of the images. Full-resolution images are around 1,500 by 1,000 by 72 in dimension, while the thumbnails are just 150 by 150 by 72. This is a big difference, and only having your thumbnails indexed could mean a loss of traffic to your site. If the purpose of your site is to sell products or display your art, this is a problem. Fortunately, there are a few things that you can do in order to get Google to index both your full-size images and your thumbnails. First, double check to verify that Google has not indexed your large images. If it has not, then you can proceed with one or more of these tips. A strategy to try for getting Google to prioritize your full-resolution images instead of your thumbnails is to code XML Sitemap into your large images. This tells Google to prioritize them when reviewing your site. You could also try using SRC and SRCSet values on the different images. By doing this, Google recognizes that they are the same image and prioritizes the larger version over the smaller one. Remember that coding with IMG is necessary for your SEO purposes. When doing the coding of the different image sizes with IMG, be sure to use the IMG tag attributes. When setting the attributes, you can specify the display sizes. Use the "ALT" attribute for this. The ALT attribute tells the Google bots and crawlers that the images are of different sizes. Setting up these specifications is part of overall responsive site design. You may want to do it so that people browsing your site on a smartphone or other mobile device can see thumbnails in a large enough size. These image settings also tell the display to adjust the full-resolution image for mobile devices. Do not forget that you will need to do this separately for each of the thumbnail and full-resolution images that you upload to the site. For more information click here https://www.reddit.com/r/SEO/comments/ap37zn/howtotellgoogleimagestoindex_full/.