Freeimage.host's API v1 (also known as Bridge API) allows to upload pictures as guest. It's called bridge API because is pretty much the same as the API from Chevereto 2.X and is the transition to the future API v2.
API v1 doesn't have rate limiting but is affected by our Flood upload limits.
API v1 calls can be done using the POST or GET request methods but since GET request are limited by the maximum allowed length of an URL you should prefer the POST request method.
API key is not public. Request an API key here