原文：http://www.cnblogs.com/shisishao/p/6000999.html

#pragma mark 獲取裁剪區域
- (CGRect)getImageRect:(UIImage *)tempImage {
    CGRect rect;
    if (tempImage.size.width > tempImage.size.height) {
        rect = CGRectMake((tempImage.size.width-tempImage.size.height)/2, 0, tempImage.size.height, tempImage.size.height);
    } else if (tempImage.size.width < tempImage.size.height) {
        rect = CGRectMake(0, (tempImage.size.height-tempImage.size.width)/2, tempImage.size.width, tempImage.size.width);
    } else {
        rect = CGRectMake(0, 0, tempImage.size.width, tempImage.size.width);
    }
    return rect;
}

#pragma mark 裁剪圖片
- (UIImage *)getCropImage:(UIImage *)image andRect:(CGRect)rect {
    rect = CGRectMake(ceilf(rect.origin.x), ceilf(rect.origin.y), ceilf(rect.size.width), ceilf(rect.size.height));
    UIGraphicsBeginImageContext(rect.size);
    [image drawAtPoint:CGPointMake(-rect.origin.x, -rect.origin.y)];
    UIImage *cropImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return cropImage;
}

[轉]裁剪圖片為正方形