Local Image Files?

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I get an "Error: Couldn't decode image" message when I attempt to use blockhash on an image file stored locally on my computer, for example "C:\Users\Bob\Desktop\blockhash\image.jpg". I have no issue with files stored online, for example "http://example.com/image.jpg". Is it possible to use the Javascript version of blockhash on local files? Is there a step I'm missing to do this? Thanks!