No doubt a good digital image is a great rendering of a document that may be difficult to read. However, it still is to your advantage to transcribe documents if at all possible, even if you have digital copies.
Transcribing a document forces you to look at every word, perhaps a word you overlooked in quickly reading the document. And there are still times where sharing a typed up transcription may be easier than an image.
When you type that document, think about what every word means. Think about what every phrase means. There may be a term upon which your research may hinge. And when you do not know what a word means, look it up. It may make all the difference.