Quick Answer, NO!
Please read this factually correct Wikipedia article.
Now let me give you a concrete example.
This image is from a web search for an Orange “Buy Now” button.
So is this one.
They look like any Buy Now button you might find on a typical e-commerce website. But if you will notice these are actually copyrighted by someone who is selling licenses for them through different online stock photo/image sites.
If you license the image from Shutterstock you can get it for $9 as part of a image bundle that will cost you $49.
Alamy will sell the single image it to you for for $49 for business use on a web page.
So what happens if you see that button on a website and you just decide to download it and use it without a license? After all its just a “common” button. At a minimum you will have to pay for the image license, however, since you used the image without a license they can actually charge you 2x, 3x, 4x, even 5x the license fee or more because you used the image without permission.
So the rule of thumb is unless you know the image is free to use JUST DON’T USE IT!
You can find free images on sites like Pixabay.com, you can purchase inexpensive images from sites like Photodune.net and pngtree.com, etc. If you search on Google and select images you can turn on Tools -> Usage Rights and select Labeled for reuse. This will greatly limit your selections but it will keep you on the legal side of using images online or in your print materials.
Don’t get caught with your license pulled down. It’s embarrassing and can be costly. I once saw a $5,000 bill for an image used improperly from Corbis.