Photographs and graphics sourced from the Internet are an incredibly useful design resource but care must be taken in deciding what to use.
Images from websites
These are normally not good enough quality. Website images are usually low resolution (72dpi) to speed up their display on screens. They can sometimes be used if the printed version is to be small or if quality is not important.
These vary in quality but are sometimes good enough. Bear in mind that many high quality Internet images are commercial products with a copyright watermark on them.