Kat, I am seeing that you have successfully posted wonderful photos to the forums in the past, for example:
The thread "Floristically Challenged Alphabet Soup: Letters S through Z." in
Garden Photos forum
So I'm wondering what has changed to make this more difficult for you. Are you using a different device?
You do have to be within a forum (not on your home page) to see that button saying "Upload an image". Maybe you're just a click away from doing what you want?
Forum options are available under "Community" in the topmost menu bar, or when in doubt you can choose the Garden Photos forum to share pics there (see link above).