I am no expert in copyright law and this can tend to be a fairly complicated subject with terms that varies between countries, so I will do my best to give my interpretation.
For photographs of instruction sheets, set boxes, promotional materials and so on, I believe the copyright belongs to the company that designed the products (LEGO for example) and not the photographer, in this case the eBay user.
I noticed that in this particular case the brand is Ritvik and not LEGO so this is an exception. So in this case it's a bit difficult for me to describe a clear answer as it's a photo of another companies intellectual property.
LEGO generally do not seem to have a problem with people sharing these sorts of things as long as it is done so as fair use and not someone attempting to scam, mislead or harm. If someone was attempting to pass of these instructions as their own, perhaps selling them as their own design, that would be in bad faith. If this was ever an issue I believe it would have been raised at some point as part of us becoming a recognised LEGO group.
The Stack Exchange official guidance is very relevant in this case, as it is mostly about plagiarism of written work.
Perhaps I could suggest some general rules for avoiding copyright violations:
- Wherever possible use your own original material.
- Clarify the copyright status, some images are available under an open licence which enables free distribution with or without modification and attribution. Google Image search for examples allows you to search for unlicensed material.
- Attempt to contact the creator for permission (perhaps more likely to work with individuals as opposed to large companies).
- Attribute the creator, perhaps including a link to the original source along with their name.
- As a last resort, avoid using copyrighted material all together. Consider if fair use of the copyrighted material is valid and adds value to the answer.