A male zebra danio will be what a "normal" picture should be. A grossly huge one will be a gravid female.
In a school, it should be easy to pick out the females. A few hundred eggs makes her much larger than the boys. Comparison of living fish is your best tool rather than by photos.
The female is in the foreground and the male is in the background, as you can see the female is much more rotund than the male.
I have a breeding and sexing page on my website, just click the link in my signature.
HTH