Disclaimer - Repeat Signage does NOT provide legal advice on copyright law for your country or worldwide. The general information below is provided as a starting point only.
The Internet is a great source of content for your presentations. For example, you can download pictures, videos, and consume RSS feeds. For example, if you had a shoe shop and had your presentation playing in your shop window, you would want to display images of shoes. If you go to the manufacturer of your shoe's website, you will be able to view and download pictures of the shoes that you will be selling. Most manufactures will not have a problem with this, as you are advertising their products. However, it would be best to contact the manufacturer and get written permission to use them. When you speak or email the manufacturer, you can also request high resolution images. Don't forget that images for website are generally low quality as the website page needs to load as fast as possible. If you stretch a small (low resolution) image and resize it to make it bigger, then the quality will go down. Starting with high quality images will give a better result.