Any counsels/lawyers/attorneys in here? Quick question re: copyright..?

Enforcement is too much hassle in most cases, but definitely it's illegal, the same as buying an ebook from Amazon and re-selling it on your own site. There is some risk in just grabbing images found in Google images search, the worst case is using some licensed commercial art a site is paying to display, some of these stock art companies are quite agressive about pursuing abusers, I have heard stories about businesses getting shut down due to the legal cost. As a rule violators will receive a cease and desist order before further action is taken, it's considered a good practice to make a citation of the image source, though it's not real legal protection.

Bear in mind it's far too simple for a copyright owner to locate their material on the internet Google image search or tineye.com will turn up most instances of an image on the internet, I searched one stock dog photo and found it in a couple of calendars and on a table top in the photo of a room.

Copyright is a type of property. The fact that someone owns copyright, like other property, doesn't automatically mean they are going to sue anyone else for "using" it.

For instance, I can let people walk across my lawn (my property) freely, or I can put up a fence to make it harder, or I can put up a sign to make it illegal. Even if there is a fence and a sign, I have no legal obligation to take names and sue everyone or have them arrested for using my property.

Copyright owners don't have to "put up a fence" or post notice for unauthorized copying to be illegal. They can choose to ignore it (or even SUPPORT it), but they could also sue anyone within 3 years of any illegal posting, assuming they first register their copyright in the US Copyright Office (i.e., shortly before they file the federal lawsuit).

Yes, it's "illegal" in many cases, not to mention a violation of the terms of use (e.g., YT), but if the copyright owners don't actually COMPLAIN about it, why should anyone else care?