I would encourage people to comment in Talk:Wiki - OpenStreetMap Wiki (“Designing policy for handling files without clear license”) or at least read through it
In general I am trying to replace images by a better one when image has a problematic license (or at least by one that is not worse). The plan is to keep valuable irreplaceable old images, just with an extra warning.
And in case of images in active use at important pages the plan is to really try to find replacements, for example see File:Mosque-al-markaz-al-islami-makassar-indonesia-6.jpg - OpenStreetMap Wiki (which was copied from source where it was deleted as a problematic) or File:Alley.jpg - OpenStreetMap Wiki (replaced by higher quality image ) or File:Calle arenal.jpg - OpenStreetMap Wiki (replaced by full sized-image found after some research). [Note: within few months this links of images being replaced will likely become invalid]
You can see what is being deleted at Category:Labelled for deletion - OpenStreetMap Wiki - click on individual images for more detail.
If after seeing info on individual page you see something that should NOT be deleted then you can comment on Talk:Wiki - OpenStreetMap Wiki and/or downgrade deletion request to deletion proposal by changing Template:Delete - OpenStreetMap Wiki and Template:Delete proposal - OpenStreetMap Wiki and commenting on file talk page.
Or here, I guess but there is higher risk of things being missed.
In some cases yes, I am simply removing an image where it was not very valuable and uploader has not responded at all (for example one of several in a gallery, used only on old abandoned proposal, used as a decoration on page about an ancient organised HOT editing activity, decoration on profile page of user inactive for years etc)
Some pictures were explicitly noted to be coming from clearly unwanted and unfree sources, in some cases they were not described and still active author only after asking revealed that they downloaded it from random website.
So sadly at least some insufficiently described images ARE copyright violations.
Some images are clear and blatant copyright violations but many are in a gray area. For example see File:PlaetzerBach BlickAufSteinrausch.jpg - OpenStreetMap Wiki - it could be easily work of uploader, maybe entire set was taken from some internet site. But if author will not respond: well, this image is quite easy to replace for cases where it is used as a generic forest and its current use on Plaetzerbachtal - OpenStreetMap Wiki is not so valuable (part of oversized gallery) and it can be removed there.
And yes, in this case I would put chances that for 99% on work of uploader and 1% on chance that it is copied from some other source. And still prefer to delete it if they will not respond.
In some cases I was genuinely unsure about copyright status of images and only at some later point there was a clear confirmation that something was a copyright violation.
Also, many, many, many images were stated to be CC-BY-* licensed, were not authored by uploader and authorship was not clearly stated. Not sure how many of remaining CC-BY-* files have this problem and how seriously it should be treated. Note that in case where image was taken by Foobar and uploaded by Barbaz to wiki then guessing that it is CC BY-SA 2.0 and stating Barbaz as author is breaking copyright law, as far as I know.
I am not aware but I prefer to avoid type of problems that may have really high costs AND are avoidable AND there is no ethical or practical requirement to be involved in them.
I am aware of cases where people had legal/financial reasons due to violating copyright.
See also “but noone will notice that I imported dataset with license incompatible with ODBL” or “they are fine with it, we can ignore all that stupid license issues and just import that data”
Do you know about
shop=hunting in your area or can find freely licenced image for it? Then help is welcome ( File:Bass Pro Shops entrance.JPG - OpenStreetMap Wiki )
Do you have photo from pharmacy in India, can find one or take one? Help with replacing File:Apollo pharmacy india.jpg - OpenStreetMap Wiki and many other images on India/Tags/Amenity - OpenStreetMap Wiki is welcome
Can you take decent image of breakwater? Help with replacing File:Breakwater.JPG - OpenStreetMap Wiki would be really welcome
You can upload images to https://commons.wikimedia.org/ and post about them in this thread (or edit file page of mentioned problematic files). If that is too complicated and found such replacement - please post here asking for help or write to me in some other way.