Or you can use the "Upload a file" button that's next to the "Post Reply" button, then follow the instructions. To do that, make sure the photo is a jpg or jpeg and not too large a size.
.
Same as Flecc use ' Upload a file ' which takes you to your pictures then select your pic and the file will appear in the bottom bar ( File name ) and then select open, once this is done you will automatically revert back to this box and you will see your file loading.