This question already has an answer here:

Probably many of you are using the Post Thumbnail feature: https://codex.wordpress.org/Post_Thumbnails

I wonder if it is possible to add a description to the post thumbnail meta box in the admin area. Such as: Please only upload quadratic images or Minimum size 250x250? Is there some kind of hook, filter or option?

marked as duplicate by Community Feb 28 at 17:33

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • Before I start copying already existing code I would suggest you take a look at this answer from @Howdy_McGee and up-vote that answer when it is what you where looking for. Or even better take a look here. Probably exact what you are looking for if I understand your question well. sorry I deleted my answer exactly at the moment you responded. – Jerry.S Feb 28 at 17:35
  • @Jerry.S It does not exactly answer my question as I wanted to add an extra labe inside the box. But for my purpose it is enough to add this information to the existing labels - (nvm repostet comment afterwards) – Blackbam Feb 28 at 17:36