Hey I'm new to itch.io and I cannot for the life of me figure out how everyone is posting pictures of their game process. I would like to do the same

I'm not sure if there's a better way, but I click the <> for HTML mode, then type <img src="http://whatever" /> for it.

AFAIK, the forums don't support hosting / pasting images directly... so you'll need to link from somewhere

I just drag them from my website and drop them into the post. It's pretty much all I use the website for from one of the free webpage sites.

I use imgur.com, then copy then image source and do the html thing.