"Students and researchers now have greater access to primary source materials for historical research than ever before. The traditional use of sources available in print and microfilm continues to be the foundation for research, but in some cases documents, letters, maps, photographs of ancient artifacts and other primary material are available online in different formats from free websites or subscription services on the internet. Users of primary sources have always needed to examine their sources critically, but now with the proliferation of electronic resources from a wide variety of web site producers, evaluation is more important than ever before. Users of web resources must now consider the authenticity of documents, what person or organization is the internet provider, and whether the electronic version serves their needs. This brief guide is designed to provide students and researchers with information to help them evaluate the internet sources and the quality of primary materials that can be found online."
Sometimes it is important to differentiate between Primary and Secondary Sources; since the the difference is often contextual, it can be hard to tell. Check the link below from the Borough of Manhattan Community College Libraries below for some clarification and examples.