Publications Handbook & Style Manual (American Society of Agronomy, Crop Science Society of America, Soil Science Society of America) -- specifically check pages 1-10 through 1-19
EndNote Online (Good to use if you use the Web of Science database often)
Mendeley (Good for storing and annotating PDFs along with the reference/citation informaiton.)
Zotero (Good for use with the Firefox browser and if you use a cite a lot of websites/webpages as sources.)
Try a search in Flickr for photos with licenses that allow you to use them without permission.
Any of the above licensing options should eliminate any "all rights reserved" images from the results list.
To see what license is attributed to a particular image from the results list
Click on the license link to view more information about the license.
For information about all Creative Commons (CC) copyright licenses, see https://creativecommons.org/licenses/
You can also use some advanced settings in Google to search for images with various copyright licenses.
However, do not assume that all images have a 'labeled' correctly. It is best to track the image back to it's original post and try to determine copyright from there.
Try these government websites for some photos and other multimedia. Generally, publications (images and otherwise) are considered public domain materials. However, this is not always the case. (For example, a department may publish a report within which they include an image for which the copyright is still held by the photographer. This is usually indicated in the caption of the photo, or elsewhere in the document.) Always confirm the copyright status of the image before you use it.