Improve your site speed and SEO performance.
Use Google’s PageSpeed Insights to test page load times and see if large images are slowing down the site.
Google recommends that your page loading time is below 2.5 seconds, but faster is always better.
Compress your images with tools such as Photoshop, Pixlr, Affinity Photo, or Kraken, and test out various image file types and compression rates to find the ideal balance of speed and quality.
Define the sizing as:
width: auto; height: auto.
For example, if your blog width is 700px, crop your images to 700px if they span the width of the page.
Use a descriptive filename with keywords that are relevant to the image and, if applicable, the page.
The filename helps provide context to search engines about your image.
Use descriptive alt text for images to increase website accessibility and to provide added context to search engines about the contents of the image.
If images don’t render or browsers use screen readers, alt text will describe the content of the image.
Captions also help readers get more context and information.