Convert image to base64 javascript on firefox

I need to convert image that are in a webpage to base64开发者_JAVA百科 over greasemonkey or firefox .xpi extension. How can i do it? I know that i have btoa() function, but i only can use it with strings, not with images. Little help here. Thanks.

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You could use the canvas element and draw the image using drawImage() onto it, then use toDataURL() to get the base64 encoded image.

see: https://developer.mozilla.org/en/html/canvas