Primary Sources are original sources: they were created by someone who participated in or observed an event. They include diaries, letters, newspapers, government documents, photographs, and other manuscripts.
These general collections include images and photographs, but most of the manuscripts are in Spanish.
Who created the image? Why was the image made? How was it created? Paint, sculpture, drawing, computer design? Why are certain characters, settings, lines, shapres, persepctives, and colors used? What do these elements communicate to the viewer? What was happening in history when the image was made? What do the pictures communicate about issues of gender, race, and class?
You will probably have to consult criticism--secondary articles and books about the image--to help you answer all of these questions.
For great ideas on interpreting images that you find, please see the History Matters page from Curtis, and this page from Library of Congress.
An increasing number of primary sources are available for free on the web. Here are some search strategies for finding them:
Strategy 1: To focus on primary sources, go to a search engine like Google, and combine your topic with terms designating primary sources such as memoirs, diaries, accounts, narratives, documents, autobiographies, online archives, correspondence, speeches. You can link synonyms together with a capitalized OR. Here are some examples:
"Pancho Villa" "primary sources"
"Mexican Revolution" accounts
Mexico "online archives"
Strategy 2: Another great way to find sources on the web is to think of a library, archives, or university that specializes in your topic, and pay them a "virtual visit" (check their web site for online collections).