Are you using the Insert Picture button just under the Bold button in the Post Reply page?
You paste a link to your pic, which is hosted on Flikr, and it puts [.img][/img.] on either side?
If so, I had this a while back, about 3 months. I couldn't even post photos in my own thread.
If this is what you are seeing, I couldn't work it out either. It just started working again after a few days.
It was incredibly frustrating. I think it was a temporary issue with permissions on where your pic is hosted as I was able to move some of mine to Google Photos and it worked for a while, until my normal host started working again.
As an alternative, you can always click the Attachments and Other Options button below the reply text box and use the Attach:Browse option to post it directly to the forum. Harder to get your post laid out nicely, and you have to have the pic on your PC, but its a workaround until something changes.
Greg