Pictures for PowerPoints
Yotophoto.com is a search engine for finding photos on various photosharing sites. Yotophoto lists the images according to copyright permission: images are either public domain or released under a ‘creative commons’ licence.
Some of the sharing sites contributing images require that you set up an account to access high resolution versions of the images, many don’t. So if you need a picture of a voltmeter, a rheostat or a brick wall for your next PowerPoint, try this site!