It is illegal to reproduce a photograph taken without the photographer's written permission.

If you take the photo to a lab to be printed, you and the lab could be liable for copyright infringement.

Purchasing prints of a photo, CD or DVD from a professional photographer or studio does not transfer the copyright of the photo to you and the photo cannot be reproduced without a release or usage license.

If photos are given to you by a third party, such as the person in the photograph, who is not the photographer, those photos are still protected by the copyright laws and cannot be reproduced either in print or on the Internet without written permission of the photographer. Receiving photos from friends or family does not transfer the copyrights to you.

You can be personally liable for copyright infringement even if you did not intend to break the law. Good intentions are not a defense for copyright infringement.

Copyright law protects photographs even if the photographer has not obtained a copyright registration and even if the photograph is published without a copyright notice.

Copyright law gives a professional photographer certain exclusive rights including the right to:
reprint the photograph
create modified images based on the photograph
sell reprints of the photograph
didsplay the image publicly

Making a few changes to someone else's photograph does not remove the copyright protection or make the modified photograph free for use.

Just because a photograph is on the internet does not mean it is in the public domain.