How to know the image cropped in GPUImage objective c

🎤 General Discussion iOS
1

I’m a new bee developing the camera app in ios using GPUImage Framework.
I’m currently working in cropping the rectangular live image to square by using the below code.

GPUImagePicture imagePicture = [[GPUImagePicture alloc] initWithImage:_image_view.image];
GPUImageCropFiltercropFilter = [[GPUImageCropFilter alloc] initWithCropRegion:CGRectMake(0.125f, 0, 0.75f, 1.0f)];

[cropFilter prepareForImageCapture];

[imagePicture addTarget:cropFilter];

MY doubt:How I can find the result whether the image is cropped or
not, because there is no outline for the crop. I tried using NSLog, the
result was print 0.0. I’m not sure what does the result mean.Please help.