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There's a lesson here for me regarding photo hosting.  Am I correct in
surmising that Flickr makes it impossible to post a simple clickable link
which doesn't require special skills or registration use?

Sounds to me like Flickr is nearly useless for sharing photos
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Flickr isn't very intuitive. You need to click on the little ' share '
symbol to get the share link to the image, but only after you have made the
image 'public'.  If it is a "private image", you can share with specific
people (but only if they have an account I think? I'm not sure about that
and I'm on mobile now and it's a pain to look it up)
Cheers from Waterloo
Claudio