Unfortunately, not all images found within the depths of the internet are permitted for reuse. Not citing images when using them or searching for images that are labeled for reuse can result in legal action against you.
There are a couple different ways to avoid any situation like this-
ORIGINALS: This is the easiest way to utilize images. This includes anything that you can come up with yourself from your own ideas and thoughts. If you create it yourself, you're definitely permitted to use it.
CREATIVE COMMONS: This website is a great tool. You can search different websites, such as Google Images, for resources that are labeled okay for reuse. This allows you to find images you need and still use them fairly.
Using Creative Commons, I found three images that I am thinking about using in my slidecast.
UPDATE: I created my slidecast on hashtags and their effect on the social media presence of a company.
