Just because you give credit and link to the source of a photo DOES NOT mean you have PERMISSION to use a photo.
What is permission? “Permission” means that the OWNER of the image explicitly said, in writing, that YOU may use the image. If you cannot show proof that you have that written permission, you are likely to be on shaky legal ground.
As a journalist you can CLAIM “fair use” — but claiming it DOES NOT make it true. Fair use is a tricky, complicated standard when it comes to copyrighted images. Do not expect a fair use lawsuit to end in your favor!
Who is the owner of a photo? You might see a lot of photos on Facebook, Twitter and Tumblr that were posted by someone who IS NOT THE OWNER. Therefore, that person cannot give you permission. That person does not have the legal right to give permission for use of the image.