Starting from Premium, you can select and dedicate an image to a specific signature field in the database or a reference to a signature in a folder based on a 'Point to image file' reference.
The process for adding the signature is exactly the same as explained in the Using Images section of this Help file.
Select Signature from the object drop down box and the Select database column drop down box will become available. If you select the ID field of the connected database, the system will automatically make it a 'Point to image file' connection. It can also that your database contains the complete reference to image file locations if that is the case, please leave the Image folder location empty and set the file extension to 'Extension included in source value'.
The image folder location can be entered directly as it can also be selected by clicking on the 
button. Select the file extension of the image, we currently support BMP, JPG, PNG, GIF, and TIFF.
You can also set the format of the value coming from the database you know for sure there is no mismatch.
If the database contains the image data and you have selected the image column, the 'Point-to-file options' section will be disabled.
More information about Signatures can be found in the Using Signatures section of this Help file.
Check for more options like colors, borders, visibility, etc., the Producer Help - Designer Properties section