The correct approach to image tags may surprise you.
Here’s a reminder about why they are best optimised using a plugin.
Because of the way WordPress evolved over time from a simple blogging tool to an advanced content management system, traditionally people have set alt & title tags per image, using the media manager.
But that’s not best for SEO. Images should reinforce what the page is about, not just what the image is of.
To give an example, if you have one image that’s used on two pages, you might not want them to both have the same alt tags. So the systems I set up does an excellent job of setting those tags in the live code whenever a page is visited. It mixes the page title with the name of your site to make sure both your branding and (most importantly) what the page is actually about is being reinforced.
It’s the best approach for image tags and search engines.
(My favourite plugin for this is PB SEO Friendly Images.)