If the image exists on another server you can use the Img button to add the pic to your post. If you don’t have another service available you can use the Add Attachment button to attach a picture. That button is below the box where you type in your reply.
Here’s a screen shot that shows the button to click to browse your hard drive to add an attachment (on some browsers the button might say Choose File, or something similar).
I had the same problem a while back, just figured the site wasn’t accepting jpeg’s for a bit cause I saw no attachment click-on way to do it. Glad to see it’s back now. Thanks from all of us.