Why can't I attach an image from the Android app when posting a question on a Stack Exchange site?
Users with less than 10 rep on such sites as Stack Overflow, Server Fault, Super User and Ask Ubuntu (couldn't find a newer source) can't post images, same for Android App. Otherwise you can, I've just checked. However there's a possibility to post your image as a bare link, then someone would come and edit the post to embed the image.
(I guess you can still upload your image on some SE site without restriction, copy the image address and embed it into desired post using the syntax