All the above replies are valid as regards copyright etc, but as regards google if i do need an image i resample it in photoshop or corel then change the size slightly, and rename it just to be sure, this wont get you over the digital rights signature if there is one, but you can check for that in the image if you have it in photoshop.
A lot of times if i need an image yes i'll look at google images, but usually if i want an image of for example some signage(thats my job) i will crop the shop front out of a street alltogether, and then crop again just for the signage element.
AL