Google has an extensive collection of images available. Many of them are free to use. Start by navigating to the following website in your browser.
https://images.google.com
Type in your subject and click the search button. 
On the results page
- Click on the Search tools button
- Now you can click Size, Color, Type, Time, Usage Rights, or More Tools to search by those characteristics of the image. More Tools currently allows you to display the image sizes on the results page.
For example, if you were looking for a free to use image of a cat in the orange color you could narrow your results in Color and Usage rights as follows.
When you want to restart your search:
- Select Clear
- Then click the Search Tools button and start your search again.
