'Expand a list of headers into a dictionary.
headers: a list of [(key, value), (key, value), (key, value)]
Returns: a dictionary representation of the list'

@staticmethod
def _header_list_to_dict(headers):

    d = {}
    for (header, value) in headers:
        if header.startswith('x-image-meta-property-'):
            prop = header.replace('x-image-meta-property-', '')
            d.setdefault('properties', {})
            d['properties'][prop] = value
        else:
            d[header.replace('x-image-meta-', '')] = value
    return d
