Configuring Signature field in CF7

Hi, I have tried to setup the Signature field on a form but get the following when receiving a form submission.
I can't find any instructions in the manual or in the forum on this topic.
Any advice would be appreciated.
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Thanks, JR
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data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAABIsAAACWCAYAAABeiAg4AAAVz0lEQVR4nO3dzYt02V0H8O+fUP/B3L9g6L0O1Dq46J0BN7UQF9nYghshhMLNDLhoGYbgQuksHBGyaBxG0IXpgUFGCdoQGSKJ2AxRg1HsSZxkiC/zuLh1rHNv3aqut+6q6v584PI8fV/OPVXdqy+................

Hi jross,
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There is a FAQ here for converting this string back to an image. It has examples for CFv5 and v6 - the basics should work for v7 but I imagine that the code will need to be tweaked :-(
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Bob