<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def set_img_path(instance, filename):
 """ Sets upload_to dynamically """

    upload_path = '/'.join(
        ['img', instance._meta.app_label, str(now.year), str(now.month), filename]
    )
    return upload_path