If my memory serves correctly (and I think it does) image itself doesn't affect your ranking, however, the image description will provide a few keywords for Google. The old saying "a picture is worth a thousand words" apparently doesn't apply to Google . If any more seasoned SEO experts know otherwise please correct me.
How do they help exactly? Even if your image has all sorts of keywords in it (ie boat_rides_in_new_york.png) I doubt it will ever be used as a reference point to any of Google search queries.
Yes they do help. Google will often put image search results within the main search results, so it can help get you traffic. Then of course, you also have people that will use Google Image search, so if you rank highly with your image, that is more traffic.
Up until 2013 that was probably the case. Back in 2013 they changed how the images were showing in the image search results. As a result, a significant amount of websites lost their traffic coming from image searches: http://www.definemg.com/how-googles-image-search-update-killed-image-seo/ There was a recent algo update that negatively impacted traffic coming from image search results even further: https://www.seroundtable.com/google-image-search-update-23436.html So, I wouldn't rely heavily (or at all) on images when it comes to SEO. That's not to say we shouldn't follow good HTML / attribute practices regarding images.
exactly one of my site was getting around 200 visits a day from images a couple of years ago and don't get anything more than a few hits a day now via google images
I guess it could not help in SEO. Even if you write keywords as name of Image it will not improve ranking. You can write keywords and source into image description but it hardly improves ranking.
Images with alt tags helps SEO practice in terms of telling the search engines what the images is all about.
You probably won't get a ton of direct traffic from it but if you follow the guidelines (mainly concentrating on having proper alt tags) it definitely won't hurt. In the end, the post looks better with an image, it may keep the reader longer on the page and you could probably throw in a few more factors that have an indirect but positive impact on your overall SEO efforts.
Actually, they do. Because right now people prefer to read content with images than just any other article. A catchy image will definitely bring hit to your article.
Images and Alt Text and SEO. We all know that search engines can't really see images (well, Google kinda can nowadays) — they have no idea if animage is of a puppy or a taco, so the alt text is how you communicate this to the search engines. Technical Services
From technical side, it is not the most effective SEO tool, but from the traffic side it will affect SEO so much. In the conclusion use more images and less text)
Not much, although some claim it did help in getting traffic at some point. When it comes to SEO I don't think it holds a lot of value even before.