Import alt text in set_post_thumbnail

Question

I am using set_post_thumbnail in order to programmatically attach an image to my posts.

I was wondering how to set a different alt text for this image, for every post, meaning that the same image might appear in 2 or more posts, with a different alt text.

Answer 1

Got it - update_post_meta has to be used for _wp_attachment_image_alt

Answer 2

You have a global alt (meta) value associated with an attachment(viewable when managed via "media" in the admin) that's stored in the post meta table, but on a post by post basis, the alt value you set when you use that piece of media into a post is stored more literally as a portion post content HTML.

The issue i think is that WordPress doesn't respect the global(main) attachment alt value and will update the attachment meta when you insert it into a post and set the alt text, whilst the specific post alt text (post content html) for that attachment will be whatever you set it to at the time it was inserted.

By calling update_post_meta on _wp_attachment_image_alt all you'll likely to achieve is a short term fix for setting what the current alt value is, it will likely change the next time you insert it and set a differing alt value.