Actually, you don't (sorry RRSODL):
In the 'Post reply' box I'm typing in now, there is a toolbar at the top with Fonts etc. One of them is a paperclip for attaching. Click it and the 'Manage Attachments' box comes up. Click 'Browse' to find your picture, then 'Upload'...now wait a while....and some more and then.....a tad longer and if your file size is within the limit you'll see all of a sudden a little File attached kinda blue writing. If you then preview post you'll find your picture's there in glorious Technicolour (unless its a B&W photo...).
So easy, even I can do it!