Fairey says he used the AP photograph as a reference, but then changed it greatly for his own idealized and colorful picture of Barack Obama.

VOA: special.2009.04.08

The problems that Frost's poetry poses for us as readers are not problems of reference. They can't be solved by footnotes.

他的诗歌给我们的困难,不是参考的问题，它们不能就用脚注解决。

耶鲁公开课 - 现代诗歌课程节选