In general when someone posts a picture (or a link to one) it is in a folder on a server (i.e. computer) on the web. If any of the following scenarios occur, the link gets "broken" so to speak:
(a) The website where the photo is located expires (host/domain expiration)
(b) The name of the original picture changes
(c) There is a change in the web address where the picture is located
(d) As you said yourself, the photo gets removed...
Kind regards,
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