You don't need a hosting site. You can upload from within the browser app, either from your PC/ Network or from a URL. It's simple; just click on the insert image button in the quick reply box. You can insert video and/ or images.
This image was posted from within my Chrome browser on OS X....don't need image hosting, mobile app or anything else. If you want to post an image of your home screen, you can do it from within the mobile app, or e-mail the image to yourself and post from your PC/ Mac.