Is it plagiarism? You are working on a Power Point presentation to report program results to your client. To liven it up, you capture a funny photo you found on the Web for your first slide.
Answer: Yes, it is plagiarism, unless you provide an acknowledgment somewhere in your presentation of the source of the photo.
Note that this question is about plagiarism and not copyright infringement. While it is not a violation of copyright to use such a captured image for educational purposes for one class, it may be a violation to use the image in a setting with a larger audience or with the potential to make money. You definitely would be violating the copyright if you published the presentation with the image.
How do you fix the plagiarism problem?
Get in the habit of adding a list of acknowledgments to every presentation. You can include sources for images and video as well as thanks for the people who helped you. See PRSA Professional Standards Advisory #16 for more information about plagiarism and copyright. Also see Professional Standards Advisory #14 on the Expropriation of the Intellectual Property of Others: https://www.prsa.org/AboutPRSA/Ethics/ProfessionalStandardsAdvisories/
Hold on! Many photos posted on the internet are FOR public consumption – free from monetary compensation and from acknowledgment. The better answer is to learn first if the photo was put into the public domain for such free use with or without acknowledgment requirements. You can tell many times if the photographer or company has its name scrawled across the photo. Stuff in public domain is presumed to be free of obligations unless it specifically indicates otherwise. Research, research, research. Then decide. Try thinking "gray area" rather than black and white too quickly. It's that way with ethics, law, copyright use, and other protections. I hope the ethics IQ score depends on using the answer "depends" for some cases. Teach analysis, not rigorous adherence to worded canons.