Based on the responses you have made:

The flag is most probably Torres Strait Islands
The Torres Strait Islander flag is attributed to the late Bernard Namok of Thursday Island. The flag is emblazoned with a white Dari (headdress) which is a symbol of Torres Strait Islanders. The white five pointed star beneath it symbolises the five major island groups and the navigational importance of stars to these seafaring people. The green stripes represent the land, the black stripes represent the people, and the blue the sea. The flag as a whole symbolises the unity of all Torres Strait Islanders. As with the Aboriginal Flag, the Torres Strait Islander Flag is beginning to be flown more widely and gaining more recognition as indigenous issues gain more prominence in Australia. The Federal Government initiated steps in 1994 to give the flag legal recognition. After a period of public consultation, the Government decided in July 1995 that the flag should be proclaimed a "Flag of Australia" under section 5 of the Flags Act 1953. The flag was so proclaimed by the Governor General of Australia, William Hayden, on 14 July 1995.
IF on the flag the Southern Cross is not visible
AND on the flag there is no Union Jack present
AND the field of the flag is blue and green horizontal stripes
THEN the flag is most probably Torres Strait Islands.
Calculated Certainty Factor: 0.77 = most probably 