Try to use:
I've tried with cacheable="false" but it still doesn't work. I'm working with reRender right now and if I refresh the page the actual image is displayed.
I want to avoid refreshing the whole page because then it jumps to the beginning of the page.
chacheable="false" allows you to turn off server caching but browser tries to show old picture anyway if the value of mediaoutput is the same between requests.
check demosite sample. There we've solved this problem already using f:param inside media output which value always different.
ok ... thanks :)