If you are searching the web looking for images here are a few tips to keep it legal.
One of the best ways to find images is on Google Images. It's fast and it's free, but to keep these images copyright free use the Google Advanced search settings.
One of the search criteria is "Usage Rights." It allows you several options and one is "labeled for commercial reuse" this is the option you are likely to want. Here is a short video tutorial on Google Advanced search using "Usage Rights".