The image should be relevant to your article. The name of the file should be relevant to the content of the image and be of the form: main-keyword-secondary-keyword.jpg
The image should be served at the size it will be displayed
Use srcset for responsiveness
Serve compressed image if possible in webp.
The number one SEO factor for images is the file name. It should have a structure such as keyword-secondaryword-index.jpg
The image URL is also important in giving context for the image to the search engine.
Create good URL structure for your images: Google uses the URL path as well as the file name to help it understand your images. Consider organizing your image content so that URLs are constructed logically. Google Images Bet Practice
Use structured data for your content and include the image :
"name": "Reguleeritav kontorilaud",
"description": "A compelling descritpion",
Alt description and title should contain your keyword but it doesn’t seem to be a major ranking factor.
Title and meta tags for the image are used by google to generate title and snippet for the image this might impact the click through rate. Most of the job regarding CTR must be done by the picture itself but I sometime use snippet to verify that the picture I am interested in is actually the right thing in the right context (imagine checking picture of clelbrities, you might sometime stop and check if that picture is actually from the celebrity, or if that product picture actually match the exact model you were interested in.
Google Images automatically generates a title and snippet to best explain each result and how it relates to the user query. This helps users decide whether or not to click on a result.
We use a number of different sources for this information, including descriptive information in the title, and meta tags for each page. Google Images Best Practice
About image quality:
Don’t use images that are too small or have a low resolution on the mobile version. Small or low-quality images might not be selected for inclusion in Google Images, or shown as favorably when indexed.https://webmasters.googleblog.com/2020/07/prepare-for-mobile-first-indexing-with.html?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+blogspot%2FamDG+%28Official+Google+Webmaster+Central+Blog%29