Copyright is copyright. If I recall correctly, if an image is made by someone it is automatically copyrighted most places unless noted otherwise.
In a lot of countries you can be held liable.
It's more about whether it's worth their time and effort. We've taken images from google plenty of times and never had an issue. I've seen multi-million dollar companies do this and never get sued. It often goes unnoticed.
If you want to be safe though google "stock image sites" but you'll need to pay a little.
In the end - it just depends.