Embedded Image

Embedded image is a URL scheme which lets you embedded the image data direct into the page/script content. The format is supported in FireFox, and largely used in GreaseMonkey's user script. IEScript support this feature which hacking technique for Internet Explorer.

The basic format of an embedded image is

data:<mimetype>;base64,<data> <mimetype> needs to be replaced by the mime-type of your data (image/png for instance) and <data> is the base64 encoded string of the actual bytes of the file. Here is an example of embedded image in gif format and base64 encoded:

<img src="data:image/gif;base64,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">

Limitations on IEScripts:

The embedded image format can only be used in user scripts, embedded image cannot be displayed in a normal web page even if you have IEPro installed.
LF/CR is not allowed in the image data part
JavaScript '+' operation is not allowed in data part
False Example:
src="data:image/gif;s4gCOVvv6" + "QoEzUtV4QGOAK+wI" + "...";
Escape char (\) is not allowed in the image data part
False Example:
src="data:image/gif;s4gCOVvv6\'Szqdjv6F....";
Only base64 encoding and the standard %xx hex encoding supported
MIME type must be specified

Further Readings:

http://www.ietf.org/rfc/rfc2397.txt