//圖片轉換成data

    NSData *imageData = UIImagePNGRepresentation(ima);

    NSString *dataStr = [NSString stringWithFormat:@"%@", [imageData base64EncodedDataWithOptions:0]];

    NSLog(@"ImageData == %@", dataStr);

這些方法可以幫助你輕易的將NSData物件轉化為Base64，或者將Base64轉化為NSData object。見以下的例子：
 NSData* sampleData = [@"Some sample data" dataUsingEncoding:NSUTF8StringEncoding]; 
  
NSString * base64String = [sampleData base64EncodedStringWithOptions:0]; 
NSLog(@"Base64-encoded string is %@", base64String); // prints "U29tZSBzYW1wbGUgZGF0YQ==" 
  
NSData* dataFromString = [[NSData alloc] initWithBase64EncodedString:base64String options:0]; 
NSLog(@"String is %@",[NSString stringWithUTF8String:[dataFromString bytes]]); // prints "String is Some sample data"