When using images in your work, make sure to give proper attribution to the owners of the creative works, just like a reference in a paper.
Check with the citation style that you are using, or use this template below:
Creator’s last name, First initial. Middle initial. (Role of creator). (Year of creation). Description or title of image. [Type of work]. Retrieved from URL.
Just because you found something on the web doesn't mean that it's freely available to use.
Resources to help you find Creative Commons images for your presentations: