Thanks @RickCarlino for your answer.
I found later this post witch is useful.
It appears that the API call to my.farm.bot/api/images only gives the 100 last pictures, it might be a problem later for what I’m planning to do.
I needed to generate images to store on my development server, but my test Raspberry Pi hasn’t a camera 
.
So I create the Fake-Camera Farmware 