Use a site that has the .jpeg or whatever at the end. I use Imgur in my phone's browser (the app sucks now since the update) once I find a gif or pic I want to post here. I select the content, highlight it to pop up options. One of them should say view, click on that. It will open the image in another window. Select the url in the toolbar and copy it. Paste it here in the b/net url bar and it should work.