To upload an image to imgur.com in Objective-C.

uploader.m

NSString *clientID = @"your client ID";
NSString *XMashapeKey = @"your key";

NSMutableCharacterSet *allowedCharacterSet = [NSMutableCharacterSet alphanumericCharacterSet];
[allowedCharacterSet addCharactersInString:@"-._~"];

NSString *base64 = [imageBinaryData base64EncodedStringWithOptions:0];
NSString *escapedBase64 = [base64 stringByAddingPercentEncodingWithAllowedCharacters:allowedCharacterSet];

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"https://imgur-apiv3.p.mashape.com/3/image"]];
[request setHTTPMethod:@"POST"];

NSString *postString = [NSString stringWithFormat:@"image=%@", escapedBase64];

[request setValue:XMashapeKey forHTTPHeaderField:@"X-Mashape-Key"];
[request setValue:[NSString stringWithFormat:@"Client-ID %@", clientID] forHTTPHeaderField:@"Authorization"];
[request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
[request setValue:@"application/json" forHTTPHeaderField:@"Accept"];
[request setHTTPBody: [postString dataUsingEncoding:NSUTF8StringEncoding]];

NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];

NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
    if (error) {
        NSLog(@"%@", error);
    }
    else {
        NSLog(@"%@", response);
        id obj = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];
        NSLog(@"%@", obj);
    }
}];
[task resume];