In order to analyze primary sources, you need to know the historical context of when a primary source was created. You should be aware of the following.
For example, if you are studying African Americans during WWII, one of the terms you should use in your searches is “negro” or “negroes.” Even though this is not an accepted term today, it was once commonly used.
When you look at the database record, you will see the term “negro” used in the photo caption, but nowhere in the record do you see the term “African American.” If you only searched on “African American,” you would not have found this photo.
Another example during the WWII era is the term “filling station” which was once used for “gas station.”