Make sure the file size is no greater than 100KB. If it's bigger than that, edit the photo by resizing it which will in turnreduce the file size. Once that's done, look in the lower left corner of the text box that you use for typing your message. Just below the text box you'll see "Click here to upload!". Click that, select your photo and upload it. Also check the "Embed picture in post" box. That's it...