You are NOT free to use any image you want from the Internet!
Not all images stored on the Internet are free to use at your own will. The owners of these images have rights that protect their work from being used without permission. You must ONLY and ALWAYS use images for which the owner has granted such permissions.
Copyright (dictionary.com) -
Legal protection given to published works, forbidding anyone but the creator from using them.
Public Domain (dictionary.com) -
Published work that may be used freely by the public because the copyright has expired.
Creative Commons (creativecommons.org) -
A license obtained by the owner to allow individuals, but not companies, to use their work.
Keeping this in mind, you MUST use websites and / or search tools that ensure you are using pictures that you are legally and ethically allowed to use.
Some Public Domain and Creative Commons resources: