I have noticed it this year. More and more photos that I want to copy and paste into the forum (to allow our users a quick view without labourious scrolling through slides etc) are deprived of typical jpg file extension. When I paste them into the forum, they work for some time and then disappear. It has already happened a dozen or more times within a few weeks.
Is it a new strategy of websites to avoid sharing their photos with others? If so, you should know about it and not complain coz nothing can be done with it.