'''Syntax:'''	'''image_filter''' off '''image_filter''' test '''image_filter''' size '''image_filter''' rotate 90 | 180 | 270 '''image_filter''' resize ''width'' ''height'' '''image_filter''' crop ''width'' ''height''
'''Default:'''	''off''
'''Context:'''	location
'''Reference:'''	[http://nginx.org/en/docs/http/ngx_http_image_filter_module.html#image_filter image_filter]