def find_start(file_data):
    """Search the image for the start of raw data 'BCRM' marker"""
    # Search the file for the start of the raw data
    raw_start = file_data.find(b'BRCM')
    #check if flag was found
    if raw_start < 0:
        raise LookupError('Flag "BRCM" not found in jpeg data. File contains no raw data')
    return raw_start