Will work even on past images?

Hi, it renders alt text from the main title of the image in the media library, so no settings are changed in any way, it only adds alt text into the HTML code of the image that gets inserted into the post at the time of inserting it. It also filters images used in theme templates, such as category pages, to add alt text the moment the thumbnail HTML code is rendered.

It doesn’t backdate images that were inserted into posts before the plugin was installed – this would involve editing the post HTML which could annoy people who have already hand-crafted the HTML of their posts, so you will need to install & activate the plugin then re-insert each image that has a title in the media library but lacks alt text in the post. Any images inserted prior to WP 4.7 will have had alt text inserted in a similar way to how this plugin does it, so you only need to re-insert images that were inserted into posts since the time of updating to WP 4.7

It’s very safe, don’t worry, as it doesn’t change any settings, it only adds alt text to the outputted image HTML in 2 ways:

* on the fly for template pages (such as category pages). so no settings are messed with (so you can always deactivate the plugin and it will be like it used to be)

* at the point of inserting an image into a post, so where the image code is inserted into the post, there is some alt text there too. insert an image into a post after activating the plugin and see the difference. deactivate the plugin at any time and only the posts that you’ve inserted images into since the plugin was active will remain affected (by having alt text in the images that were inserted since the plugin was active)

so it’s really quite harmless, and yet very important for seo. without alt text google will be clueless what your images are about.