SourceFile tag data is not currently used (source_file is set up but does not appear to be used).
When the PNG file is converted to JPEG and annotated, it should save the value of source_file and not the PNG file name. The tag will need to be stored in the JSON file in order to enable this.
Allow the use of any size of image. Command line or JSON parameters to determine how clipping or embedding should occur given a width and height value. If the width and height values are not given then the largest file is used to derive these values.