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Here is the link I found regarding document checklist for N-400.

是否我有理解错误，还是USCIS刚更新过？

-I don't know, but this USCIS link say the two photos are needed:

https://www.uscis.gov/forms/citizenship-and-naturalization-based-forms/document-checklist-form-n-400-application-naturalization

You had better read the N-400 Instruction which is more formal than other USCIS website.

谢谢！