Do not use images you find on the internet
Using Google image search provides an entirely arbitrary mix of images that can be both free-use and copyrighted. Avoid finding images that way. Using images to which you do not have rights can result in a hefty bill suddenly falling into your inbox.
Safe image sources
Safe ways to find usable images is to use free sites with so-called "commons." There are images without rights (aka public domain) or images available for free use as long as you credit the photographer or photo base. Examples of this are the websites Flickr and Wikimedia. Here it is written on all the pictures what requirements they have.
A safe alternative is to take a picture yourself. Or you can borrow from someone else from whom you get permission.
Photos must generally always be credited. Images are intellectual property, as are compositions. The exception is when they are entirely "public domain."
The universal design of images
Pictures must have an understandable title and alternative text to be published digitally. Read more about universal design.