The CC licensing requires attribution for any content that isn't your own, including images. People often post unattributed clarifying images copied from somewhere else. It is clear from the post that they are not taking credit for it, so plagiarism doesn't apply. But use of the images doesn't meet the license requirements.
New contributors are typically informed and given time to add the attribution. On questions, they often leave after getting an answer and don't bother fixing the attribution. Other users will sometimes do a reverse image search and add the attribution if found, but it often can't be found that way.
This presents three related questions:
If the image creator can't be identified, the identification attempt is shown by adding text to the effect that the source is not identifiable. The thinking is that should the originator become aware of the usage, they could identify it as theirs, and it would be clear that an attribution attempt was made. Is this adequate to meet at least the spirit of the license requirements?
If #1 is not adequate, or nobody wants to invest the time to identify the image, we have a thread with a question and answers. How far do we need to go to comply with the license requirements? For example, if we hide the image, the post usually becomes too unclear to be useful. If it's a question and we hide the image, the answers become non sequiturs, which is unfair to the answerers. If the image is in an answer, the answer may become too unclear to be useful. So hiding images, means closing/deleting posts, which removes otherwise good and valuable content.
Should questions containing unattributed images be immediately closed pending attribution when it's noticed before answers are posted (would result in very unequal treatment of posts depending on how fast answers are posted and when people notice the missing attribution)?
What's the appropriate way to handle unattributed images that are not plagiarism but don't meet the CC license requirements, and how far do we go in removing or degrading content to comply with the license when the OP does not?