Yes, we all seem to experience trouble with photos. I wonder if there's any way that could be changed? The site is a pretty popular one.
I'm no expert but this is how I usually do it.
If it's an online image - on google images or similar -
Left click on the thumbnail - when it bring it up right click on 'copy image location' then in the reply box on this sight select the image button ( below underscore) [img] [img] and left click between the 2 image boxes and select paste. The code should end in .jpg.
If the image is on your computer you will need to upload it onto something like Picasa, Photobox, Google + photos. Then click on the thubnail - when it brings the image up right click and select 'copy image location' then paste it into the reply box as before. You can't paste an image straight from your desktop ( at least I haven't found a way yet.)