Images with a CC0 license or images in the public domain do NOT require a credit. They are free to use without attribution unless including credit is a requirement of your assignment and is required by your instructor. CC0 images are an excellent option for brochures and posters.
Assume the content you find is protected by copyright unless there is a statement that states otherwise.
You can filter your image results to show only images that are labeled for reuse:
1. Type your search terms into a Google search box. Select Images.
2. Select Tools – a new menu bar will appear below.
3. Select Usage Rights from the new menu bar and then select Labeled for reuse.
4. Your image results will now be filtered -- Results include only images Labeled for reuse.
5. Click on the image, until you land on the webpage where the image is hosted, to confirm that the image can be used. Look for the name of the creator and usage terms or a Creative Commons (CC) license.
NOTE: Please do not use the BING search engine. The filter tool in Bing does not work as advertised.
Bing filtered image search results consistently include copyright-protected content.
Consider searching for images from public domain repositories or images with creative commons (CC) licenses. Open source and CC images are free to use and share.
See the Finding Images tab for more information.
Reverse image web searching tools may be able to answer this question.
Royalty Free does not mean no cost.
A royalty based fee schedule requires ongoing payment based on the number of times the content is used.
Royalty Free means a single payment (the permission fee) covers multiple use of the image without additional payments. It allows for more than one use of the image for the fee paid.
You pay for the image, but it is free of royalties or ... royalty free.