You need to find an online web service to host the photograph and upload your picture to your chosen site. Photobucket is an example site, but there are others too.
Once your photograph has been uploaded, you should be able to get a URL or it's web address for sharing and viewing just the photograph. Use the icon that's above the text box when creating a post and paste the photographs web address into the box that appears when the icon is selected.
Hit 'OK' and the photo should be added to your post.
You can always use the yellow "Preview Post" button to check if you've added the photo correctly before posting.
Please though, keep the resolution to a medium size as many post photographs on here which are far too large and make viewing awkward.
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