Updated: May 11, 2019
All images, including logos, should be optimised for SEO. Images help drive attention to the page, especially those that are eye-catching.
Sadly, search engines cannot process images, and they rely on the title that you give the images to understand what that particular picture is about.
For instance, images should have a relevant filename. You can use a keyword that would reflect what you want that image (or page) to be about as the title.
For example, DSC_4134.jpg is not as effective as daybed-elwood-melbourne.jpg for SEO, the latter of which clearly conveys that the image is of a daybed in Elwood, Melbourne.
Images should also be resized or scaled for SEO as well. This means that your image should not be too big so that the file size is huge, creating delays in load times on browsers and mobiles.
Never get a photo and leave it as it is without resizing it to fit your content. Resize and maintain the aspect ratio, and/or crop the image to capture exactly that which is relevant to what you want to communicate through the image. Less is more because if your site doesn’t load fast enough you lose viewers.
Everyone wants a good user experience when going to a page. You don’t have to save in the highest quality photo format when you’re saving for the web. A 7MB photo could likely be resized to a 700KB photo by saving it as a lower-quality JPG.
Rule of thumb: -photographs are best saved as JPGs – logos (single colours) and screenshots are best preserved as PNGs (or GIFs, in a save-for-web format).
When the image is ready to be uploaded, make sure to take advantage of captions and alt text/title text. Captions are the text that usually is displayed below the image and gives a descriptor of what the image may be about.
This is important because people (and search engines) like to use the text when scanning an article. Not all images need captions, but where relevant, it’s a nice addition to have.