SEO concentrates a lot on written and/or textual content. There are literally millions of sites out there that promise to make a website SEO perfect, based on the text on the page, the META data and many other things, but rarely is the photography touched.
So why concentrate on that now? Many reasons are there to start looking closely at the picture content on the site and how it affects SEO. First, not many people do it. The search engines base their many rules on the way that people interact with sites and the methods that people use to try to cheat the web crawler. Early SEO could be manipulated in many ways and the most popular methods of manipulation became the first rules applied by the search engines as negative.
The closest that most website owners and/or operators go with SEO is using social media to link pictures to their site. That may be the end of the line for those sites, because many times the images linked back to the site have nothing to do with the site itself. A fancy little cat meme is stored on a back page of a site, so that the heavy social media traffic will boost the site. This is a hit and miss method and sometimes works well for a site. The actual image was chosen, linked to and used in no greater depth than its popularity.
Most image SEO begins behind the scenes. Sometimes simply the way that the tag is used can affect the relevance of the image to the page. Caption is one of the most important facets, as not only does the text appear on the page with a “hover” the text is in the tag itself. More and more each day the search engines are being used to find images. This was once a nerdy thing that was slow and not very useful. Now, the search engines have stepped up the game and most mobile phones can search the engines for images with very little lag. That is why tagging the photos properly can be so important.
Sharing in social media of an image is one thing, but when a person searches for an image to download for a purpose, the image type may be specified and that gives the web developer yet another aspect to consider. PNG is very popular because of the transparent background.
Simple, start by using a good, clear image file that works well on the site and looks good. Use the caption and other tags properly. Make sure that the tags are correct and match the image, the page and the use of the image. Also, store multiple sizes and file types of the same image in the same web server folder. These should all use the same tags. This is useful when an image search is done. Your various formats and sizes may come up with different searches. Lastly, downloading is not that bad of a thing sometimes, at least there was a hit on the site. There is a script or two out there that does automatic water marking and there is even one we have seen that only water marks the files as they are lifted from your site.