DNN module - Can I pass in an arbitrary sized input ?

edit

You could simple try. But the right answer is NO, you should pre scale image before input:

cv::Mat cropAndResizeFromCenter(const cv::Mat &input, const cv::Size size)
{
    cv::Rect roiRect(0,0,0,0);
    if( (float)input.cols/input.rows > (float)size.width/size.height) {
        roiRect.height = input.rows;
        roiRect.width = input.rows * (float)size.width/size.height;
        roiRect.x = (input.cols - roiRect.width)/2.0;
    } else {
        roiRect.width = input.cols;
        roiRect.height = input.cols * (float)size.height/size.width;
        roiRect.y = (input.rows - roiRect.height)/2.0;
    }
    roiRect &= cv::Rect(0, 0, input.cols, input.rows);
    cv::Mat output;
    if(roiRect.area() > 0)  {
        cv::Mat croppedImg(input, roiRect);
        int interpolationMethod = 0;
        if(size.area() > roiRect.area())
            interpolationMethod = CV_INTER_CUBIC;
        else
            interpolationMethod = CV_INTER_AREA;
        cv::resize(croppedImg, output, size, 0, 0, interpolationMethod);
    }
    return output;
}