Which of the following sources is the most likely to provide a historian with credible information about a historical figure

So you haven't linked the sources so I can't directly answer your question, but I can give you some advise on finding credible sources

The first thing you need to identify is the website or place where you found your source. Analyse this place and find out if it is credible and trusted

Secondly, if this is a piece of text, find out who wrote it. It is important to understand the writers relation to the figure, as it will help you understand if he/she is biased in anyway. Although, sometimes a biased opinion can be usefull. For example, an autobiography probably won't give you the most reliable "facts" but it can help you understand the ideology of a person.

Finnaly, photos are probably the most usefull sources. Assuming you got the photo from a reliable place, it will most likely not be altered. Photos are also just presentation of facts and information which leaves no room for bias