>>> def filter_jpeg(filename):
	f=open(filename, 'rb')
	d = f.read()
	f.close()
	if '\xff\xc0' in d: return 'Baseline'
	if '\xff\xc2' in d: return 'Progressive'

	
>>> filter_jpeg('c:\\temp\\1.jpg')
'Baseline'
>>> filter_jpeg('c:\\temp\\2.jpg')
'Progressive'