Now you should understand why musicians are always getting bent out of shape and copyright lawyers are always swarming over any new hit song.
At least with the written word there are many great tools to detect intentional plagiarism. For images we now have Google image search. For audio and video you upload to YouTube and wait for the DMCA copyright take down notifications...
Yes, nowadays we have some useful tools to detect plagiarism. But this is different, this is about the difference between what is a copy and a theft, and why :)
Got it - I was trying to point out that intentional and unintentional copying or "derivation" is everywhere but people may not realize it, they may not even realize they are doing it, even if intentional. So if you're sensitive - because it was your original work that got re-used, or because you are incentivized to find copies (lawyers) then you will probably see copies everywhere.
I think at least one example you gave - the Dodge Ram vs. School Ram clearly has an almost identical if not actually identical image that is common. It could be that there was a stylized ram image that is in the public domain or licensable and they both used it. Or someone from the school intentionally copied the ram not thinking anything of it (I'm almost certain Dodge would come after them if the find out) or someone cut the ram image from the Dodge logo and posted it online without attribution - maybe with a creative commons license to boot.
There's actually a story about the Dodge logo here: http://www.npr.org/templates/story/story.php?storyId=123781334 - it never mentions who created the logo originally but even seems like they actually knew it was the same already.
On point :) and probably something very similar already existed before the Dodge and school logos ;) thanks for sharing the story :)