lets say you want to use this photo . If it has a watermark, feel free to use it as long as it stays on! If it doesn't, here are some examples of how to cite it:
option one: Photo Credit Katrina Craig, www.katrinacraig.blogspot.com
option two: Photo Credit Katrina Craig
if i have cited my work as being someone elses, simply replace my name with their name and still put a link to my website (in this case i was emailed a photo and it does not have a direct source online).