ed_f wrote:
does that mean that „description“ just isn't seen by a searchengine at all? i.g. I do not change my filenames.
If the page that the image is on contains additional related information about the image, then this can be considered the images "description". In the case of X3 images in the sitemap linking to the image landing page, that page will of course include the image's description. What Google makes of this is up to Google, but as noted previously, it will look at the image, image name and the text/context of the page the image is on. This text/info may then be used to display the image in search.
You might be overcomplicating? It's quite straight-forward. Let's search for a bird "black-capped chickadee" on Google > Images:
It will show images that best match the search, with images on pages that display best information about the subject, on websites that have collected authority and rank through popularity. Clicking the image will show an enlarged version, which links to the page that contains the image, displaying text and meta data from the page.
The image url itself is just a name, with very little info.
https://upload.wikimedia.org/wikipedia/ ... 69%29.jpeg
The reason the image is listed so high, is because it's then linked to a page with perhaps the best information about the image search, in this case Wikipedia, which carries much authority:
https://en.wikipedia.org/wiki/Black-capped_chickadee
For Google, there is no such specific thing as "description". It will find images, and then rank them based on the subject of the image, and the related content on the page it's on. In this example, it will find a lot of information on the target link specifically for "Black-capped chickadee", thus it will rank very high.
One thing is getting your images indexed, another thing is being able to rank high in search. It's almost impossible for private websites to rank high on generic search, unless your website covers unique search phrases.
With X3 when using the sitemap, Google will find your image descriptions on the "image landing page" and possibly use it to compliment the image in related search. There is no such specific thing as "image description" for Google or other search engines.