Two things I stumbled on to get the pic posted:
On the Imgur image page, towards the top. there's a little window for "Auto Resize". I opened that, and chose, I think, size for forums. It's about half the size the pic is at when it's imported to Imgur; you see this as a number, not an image.
Also, I needed to click on "Preview", bottom right of the posting page... wait till the pic appears on the screen... and post.
I need some practice.