Flickr is a huge repository of photographs. There are some constraints associated with this collection. Many images are too small to be useful and some have restrictive copyrights. Careful searching, however, will retrieve a vast collection of photos which can be used in presentations and on web pages.
Finding and Using Flickr Images
The use of Creative Commons images fits nicely into the OSN philosophy; we share our resources for educational purposes.
Use the Advanced Search function and click in the "Only search within Creative Commons-licensed content" check box (it is close to the bottom of the page). This limits the search to Creative Commons photos. These are the photos which you can use in an educational context without violating copyright restrictions.
Be careful using Creative Commons searching. It is easy to revert into searching the entire collection.
When you find an interesting photo, note the TAGs. They may lead you to other, related photos.
Placing Your Own Photos on Flickr
Free accounts limit the size and rate of adding photos.
Paid accounts remove the limits.
Embedding Flickr Photos Using Links
The idea is to link to photos, when possible, rather than downloading the photo (which requires that you store the photo). The additional advantage is that the link allows easy access to the original photo site (which generally has other size images, comments on the photo, links to other images in the collection, and other useful stuff).
All of the Examples (found on the pages which are linked on the left) have used embedding.
This example assumes that you are going to add Flickr images to a Google Sites page.