There are a number of tools to help you find images on the Internet. To search in Commons' internal database, use Special:MediaSearch or Special:Search (see also Help:Searching). There are also several gadgets available to link to these tools - they can be activated by visiting your Preferences.

Image search gadgets

• Reverse Image Search: On File pages, adds a new tab to easily search for similar images on the Internet using Google Images, TinEye and Yandex. [documentation / talk]