You need to be able to identify who created the source. This is usually accomplished by stating their last name (e.g. "Smith"). To find the creator of a source, these general tips may help:
For some sources, however, you may not know who the creator is. As a result, you will simply have to state that it was an ‘unknown author/artist/photographer/etc.’
The Gallic Wars was created by Julius Caesar himself and it recounts his invasion of Gaul.
This statement was made by Smith, a Research Fellow at Harvard.
The image was taken by an unnamed photographer.