Image optimization is generally regarded as secondary in SEO, because traditionally what has prevailed is to concentrate on text searches and thus on optimizing text documents to respond to those searches. 
27% of web traffic generated from search engines has come from Google Photos, while 68.8% came from Google Web (text searches) and the remaining 10% came from other search engines (Bing, Amazon, Yahoo, etc). 
These are aspects of how to position images in Google:
  • file name. An image is a file that we host on our server, and that file is uploaded to our website with a file name, ending in a file extension. If it is a photo of a blue turtleneck, but the name is something incomprehensible, such as “IMG0078562.jpg” we will be missing an optimization opportunity. It would be better to call our file "sweater-neck-high-blue-01.jpg". The hyphens are important since if we leave spaces between the words, when uploading to the server those spaces will be erased and the words will be joined into one. It is also advisable to avoid non-international characters, such as ñ, since in the same way they will be transformed by something unreadable when uploading to your server.
  • Type of file. The universally accepted types are jpg, png, and gif. Recently, a new very optimized format has been added in terms of weight, the webp, although not all browsers recognize it yet. Do not use gifs for animations, a video is better, for reasons of optimization of load time (WPO).
  • Alt, title, and longdesc tags. These tags are used above all for accessibility, since if a blind user accesses our website they need to have a text description of the images, or else the images on your website will be totally useless for them. Of these 3, the most important, for influencing positioning and because it should never be lacking for accessibility, is the alt tag. In it, you must give a concise description of what is seen in the image. Avoid the temptation to spam this space with keywords if those keywords are not descriptive of what is seen in the image, as it will not help you to position better (Google has algorithms to detect and devalue keyword stuffing) and on top of that, you will not be fulfilling the purpose of helping accessibility. The title and longdesc tags are not essential, and they are used to give a title and a longer description of the images. Use them if you think they are necessary or that they contribute to your users in specific cases.
  • Context (The text surrounding the image). Google is not guided solely by the alt tag to "understand" what is in your image, since this would be very easily manipulated by those who want to spam. It is also guided by other factors commonly used in SEO, such as the text on the page, especially that surrounding the image. The best we can do to optimize this, instead of abusing keyword stuffing again, is to place the images in the relevant place on the page, that is, when we are talking about what appears in the image. If we place our images in a chaotic way, we decontextualize and make it more difficult for Google to know what is in it.
  • Using image sitemap. To make it easier for Google to discover and track your images, especially if you have a large site with lots of images, it might be a good idea to create an image sitemap and submit it to Google through Search Console. Using the image sitemap, you can specify image properties, such as its geographic location (geo_location field). To see all the specifications that you must follow, recommend that you consult the official Google documentation on image sitemaps. This goes without saying, but just in case, do not block Googlebot the location of your server where the images are since in this case, Google will not be able to access them to index them. Similarly, make sure that you do not have meta robots or x-meta-robots with the value "noindex" in your images, since that would mean that Google could access them, but not index them.
  • Structured data. For product images, if we want to see this type of enriched fragments in Google, it is essential to use the Product type markup in the URL, which includes a field for images. Check everything about Structured Data Markup for Product, directly in the official Google documentation. If, for example, you have recipes on your website, it is very important to do the same, but with the Recipe type markup.
  • Image weight and dimensions. It is estimated that 50% of the data sent to users by a website corresponding to images. Therefore, the more we optimize them in terms of weight (without losing quality and therefore compromising the appearance and experience of our website) the more we will be helping a good loading speed.
  • Own and original images. The images of your website must be hosted on your own site, not on third party sites, since then what you would be doing is using their server's bandwidth without permission, and you would also have no control over those images. They could change, disappear, and you would have to update the image on your site.
In conclusion, quality, good resolution, lighting, etc. It matters as Google's algorithms have more trouble interpreting a blurry or highly pixelated image than one with crystal clear resolution. Images with higher quality, contrast, and good composition also attract more clicks from Google.

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