在 API 低于 30 的情况下，可以通过以下方法实现 Android 辅助功能服务的截屏功能：

1. 在 AndroidManifest.xml 文件中添加截屏权限。

2. 在 AccessibilityService 中实现截屏功能。

public class MyAccessibilityService extends AccessibilityService {

    private ImageReader mImageReader;

    @Override
    public void onCreate() {
        super.onCreate();
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
            DisplayMetrics metrics = getResources().getDisplayMetrics();
            mImageReader = ImageReader.newInstance(metrics.widthPixels, metrics.heightPixels,
                    PixelFormat.RGBA_8888, 2);
        } else {
            mImageReader = ImageReader.newInstance(getScreenWidth(), getScreenHeight(),
                    PixelFormat.RGBA_8888, 2);
        }
    }

    @Override
    public void onAccessibilityEvent(AccessibilityEvent event) {
        takeScreenshot();
    }

    private void takeScreenshot() {
        // 获取当前的窗口所在的 AccessibilityNodeInfo 对象
        AccessibilityNodeInfo root = getRootInActiveWindow();

        // 获取屏幕区域的像素数据
        mImageReader.acquireLatestImage().getPlanes()[0].getBuffer().rewind();
        int width = mImageReader.getWidth();
        int height = mImageReader.getHeight();
        int pixelStride = mImageReader.getPlanes()[0].getPixelStride();
        int rowStride = mImageReader.getPlanes()[0].getRowStride();
        int rowPadding = rowStride - pixelStride * width;
        int bufferSize = width * height * PixelFormat.RGBA_8888 / 8;
        ByteBuffer buffer = ByteBuffer.allocate(bufferSize);
        byte[] row = new byte[rowStride];
        for (int y = 0; y < height; y++) {
            int position = (y * pixelStride * width);
            buffer.position(position);
            mImageReader.getPlanes()[0].getBuffer().get(row, 0, width * pixelStride);