This could be handled by the client. Get the Ruleset for image uploads (max size, format, etc.), Validate the image within the client, only upload when the post is published.
Then the delay between post and image only depends on your internet connection and the user can still take 3 hours to write a post.
I guess one issue about engineering a well performing algorithm is that ot only works if you collect a real high amount of personal data and label it with stereotype based labels. And then you have to do the same with every content shared on the platform.
If you do this publicly, people will have problems with the labels of their posts.
Your awesome idea gets labeled as left wing utopic dream? Your rant about that new movement is conservative and populistic?
Might be true, but will offend people.
There is this great overview to find the Specs and all info about upgrading and stuff: https://www.parkytowers.me.uk/thin/
India has actually developed such an open platform: the open network for digital commerce.
https://ondc.org/learn-about-ondc/
https://en.m.wikipedia.org/wiki/Open\_Network\_for\_Digital\_Commerce
So the software is there. You only need to adapt it to Europe and get people to use it.