-(void) addTapImageGesture
{
    UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapGestureAction:)];
    tapGesture.numberOfTapsRequired = 1;
    tapGesture.delegate = (id)self;
    [self addGestureRecognizer:tapGesture];
}

//这里增加手势的返回，不然会被WKWebView拦截
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer
{
    return YES;
}


-(void) tapGestureAction:(UITapGestureRecognizer *)recognizer
{
	//首先要获取用户点击在WKWebView 的范围点
    CGPoint touchPoint = [recognizer locationInView:self];
    NSString *imgURLJS = [NSString stringWithFormat:@"document.elementFromPoint(%f, %f).src", touchPoint.x, touchPoint.y];
    //跟着注入JS 获取 异步获取结果
    [self evaluateJavaScript:imgURLJS completionHandler:^(id result, NSError * _Nullable error) {
        if (error == nil)
        {
            NSString *url = result;
            if (url.length == 0)
            {
                return ;
            }
            else
            {
            //如果是url 则转换成 UIImage
                NSData *imgData = [NSData dataWithContentsOfURL:[NSURL URLWithString:url]];
                UIImage *clickImg = [UIImage imageWithData:imgData];
                if (clickImg)
                {
                    NSArray *imgArr = @[url];
                    NSMutableArray *tempArray = [[NSMutableArray alloc] init];
                    [tempArray addObject:clickImg];
                    //将图片 存起来 ，然后可以放到 预览控件里面去了
                    [self setImgUrlArrayKey:[tempArray copy]];

                   //to do 这里就可以将图片放在你想要放在的 图片预览控件里面了
                }
                
            }
        }
    }];
}

最后我们可以在 WKWebView 的 delegate 加载完成的 回调里面增加使用

- (void)webView:(WKWebView *)webView didFinishNavigation:(WKNavigation *)navigation
{
    [self.webView addTapImageGesture];
}