After some time, I do have one suggestion for image posts from a user experience stand-point. I've found that the supported (only support jpeg and png) image error pops up after trying to post a pic with that is not supported (.gif or .webp as an example.) after using the "choose a file" explorer pop, and if one was to drag and drop an unsupported file at the moment, there is no visual feedback that the file is not supported aside from the image not appearing in drag and drop area.
Maybe you're already aware of this being the site is in alpha, but I feel that a better user experience would be if that message appeared when drag and dropping an unsupported file and if an unsupported image was selected in the file explore pop up instead of appear after hitting the "Post It!" button. Just thought I'd flag it just in case.