XML results will be in the form of:

(Content-Type: "text/xml")
<result errorcode="&#91;error code&#93;">
    Description for result code (0 = ok, no error)

Optional tags can be present and the tag description can be ommited, depending the command issued (specifically if the result sends back information).
When a jpeg image is send, the result will be in the form of:
(Content-Type: “image/jpeg”)
(image data)

The Response section for every function describes the possible returning errorcodes.

All functions except those that return an image, will return an error code of 0 or greater in case of success and an error code less then 0 in case of failure. An error code of “0, Ok” means that the function is executed without error. An error code of “-18, General error” can be returned if an unhandled error occured. Consult the logging files for more explanation in that case.