Google Images can be a quick easy way to search for digital images. But Google cannot grant you any rights to use images for any purpose other than viewing them on the web. The images identified by Google may be protected by copyright.
But you can limit a Google Image search to Creative Commons images only:
Note that these filters aren't always accurate, and don't differentiate between different kinds of CC licences. It's a good idea to double-check the image directly on its website before downloading it.
You can modify Google and other search engines to look for creative commons material only. Go to advanced search in Google, and set a filter for reuse. Go to the bottom of the page to 'usage rights' and change it to the type of use you want. 'Free to use or share' would apply to classes at Monash, and 'or modify' if you plan on altering the image.
Colour based search of creative commons images, Created by Tineye - Useful when need images with particular colour.
You can also use Google Image search to search by colour. Click "Tools" and select your colour and your creative commons licence