You and your client could get in legal trouble.

Derivative work

Royalty-free image banks and Creative Commons licenses

Metadata panel

Without permission, a professor uses a copyrighted image in a relevant way in her research report.

Authors, artists, and other creators

The copyright has expired or been relinquished;; you can use it freely and without permission.

The lifetime of the creator plus 70 years

They are ensured proper credit and compensation for use of their original works.

Copyright mark, year of publication, name of copyright owner

Digimarc filter

Without permission, a newspaper reporter uses a copyrighted image in a relevant way in a news story

It allows you to copy, change, and distribute the image for commercial as well as noncommercial uses, with few conditions.

Ask permission, or don't use the image!

The "BY" license

The work could still be "discovered" and used without consent by or compensation to the copyright owner

Under certain limited conditions, you may use a copyrighted work without permission from the copyright owner.

"Fair use" is difficult to determine;; there are no hard and fast rules.

Work commissioned by an employer or a contractor, aka "work for hire"

Most images found online are probably copyrighted, and it is illegal to use copyrighted images without the owner's permission.