I just started running a PbP, and it seems like the only images I can paste in have to originate from an unauthenticated source within my browser?  IE I can't just take a screenshot or copy an image to my clipboard and paste it.  When I do that, nothing shows up at all.  So right now to paste a combat map in I have to capture it, save it, upload it to google photos, and then copy and paste it into the post.  I've tried different browsers and different machines.  Am I missing something?

You need to host the image on the hosting image service, then you can use the Insert/edit image function of the text editor.