Not sure what you finally did, but the simplest way is:
To get photos to load quickly and show in the post, you first have to upload the photo to this site.
1.) Login
2.) Go to My Account (may have hit Home button first) and down to Album
3.) Choose Upload Picture (navigate to photo you've given a sensible name to), be sure to then hit Upload.
4.) Go back to Album, click on thumbnail to open full size image. Right click (Windows); Control Click (Mac) and copy the URL, then paste same in desired thread, using the IMG tag in the compose window.
I'll close this subject out...looks like you have it figured out...