This is what I used to get picture to post. When you are submitting a post, or making a reply, click the Go Advanced button below the window you are entering your text. That will end up redrawing the page a bit so just scroll down again until you see the text window.
Keep scrolling to find the Additional Options section, and in that section is a button for Manage Attachments. Click that and it opens up a new (separate) window. In that window click the Browse... button to find the picture you want to upload. Repeat for additional images, then click the Upload button. After that (it may take a few seconds or a minute depending on # of pictures and size), find the Close this window button.
That should return you back to where you were typing text. At that point, click Submit Reply and you should be good to go. My picture was a GIF, JPG usally work better for me.
GMC Sierra 1500 SLE 5.3
2015 WH 27DSRL