Copywrite law is a minefield, with different laws in different countries.
Im no expert in this field, but in Australia, you are liable if you use an image that "belongs" to someone else. Taking the picture does not necessarily mean you "own" that image. Manipulating an image no owned is no breach of copywrite. if a picture is taken of some sort of public icon, like say the habour bridge, can never be a breach of copywrite, regardless of all the trademarks or copywrite symbols you might put on that image.
Using an image in this country for a non-profit reason in this country is no breach of copywrite. If you take an image and use it in a school assignment, the owner of that image can moan all they like, there is no breach of that copywrite.
The line is crossed if an image is stolen, with even the intent of using that image for profit or direct financial gain. If you do that in this country you can be held liable generally to the extent that image has derived gain for you.
If an image is of personal or emotional importance, and it is stolen, the thief can be held liable for punitive damages. Thats a hard case to prove however.
Government and corporations have different rules again, generally much stricter with higher penalties.
Pretty sure of that stuff, but not so sure of images that have already been poached and reposted on the internet. I dont think you can re-copywrite an image that has already been taken, except if it the result of a special permission. Using an image of a famous painting is no breach of copywrite.
What confuses the hell out of me, are where, in cyberspace, national laws can be applied to international situations.