Wow I just found Imageshack and it just does what I need. The API is very simple! Here is a working example:
First login with your username and password to get an access token
var token = "";
$.ajax({
type: "POST",
url: "https://api.imageshack.com/v2/user/login",
data: { api_key: "*****************", user: "**********", password: "*******" }
})
.done(function( msg ) {
token = msg.result.auth_token;
});
Once you got this token, you can upload an image from a URL.
var imgUrl = "http://www.scarlettjohansson.org/hairstyles/scarlett-johansson-hairstyle-3.jpg";
$.ajax({
type: "POST",
url: "https://api.imageshack.com/v2/images",
data: { api_key: "2579FJLP41717571ea15b5405adcbac60bf1dc44", auth_token: token, urls: [imgUrl]}
})
.done(function( msg ) {
console.log( msg );
});
This only has a 30days free trial. If someone has a free alternative it would be great!