name IMAGEDIRECTORY does not exist in the current context

hi

this is my code it is for resizing image 

 public string img_resize(string picname, int maxHeight, int maxWidth)
    {

        System.Drawing.Image currentImage = System.Drawing.Image.FromFile(Server.MapPath("image/house\\") + picname);

        double imgHeight = 0;
        double imgWidth = 0;
        imgHeight = currentImage.Height;
        imgWidth = currentImage.Width;

        if (imgWidth > maxWidth | imgHeight > maxHeight)
        {
            //Determine what dimension is off by more
            double deltaWidth = imgWidth - maxWidth;
            double deltaHeight = imgHeight - maxHeight;
            double scaleFactor = 0;

            if (deltaHeight > deltaWidth)
            {
                //Scale by the height
                scaleFactor = maxHeight / imgHeight;
            }
            else
            {
                //Scale by the Width
                scaleFactor = maxWidth / imgWidth;
            }

            imgWidth *= scaleFactor;
            imgHeight *= scaleFactor;
        }


        string html = null;

if (imgHeight != currentImage.Height | imgWidth != currentImage.Width) {
	html = "<a href=\"" + IMAGE_DIRECTORY + Path.GetFileName(s) + "\">" + "<img src=\"ShowThumbnail.aspx?img=" + Path.GetFileName(s) + "&w=" + imgWidth + "&h=" + imgHeight + "\" " + "height=\"" + imgHeight + "\" width=\"" + imgWidth + "\" border=1>" + "</a>";
} else {

	html = "<a href=\"" + IMAGE_DIRECTORY + Path.GetFileName(s) + "\">" + "<img src=\"ShowThumbnail.aspx?img=" + Path.GetFileName(s) + "\" " + "height=\"" + imgHeight + "\" width=\"" + imgWidth + "\" border=1>" + "</a>";

}
return html;

when i run it this error occur

Compilation Error

Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.  Compiler Error Message: CS0103: The name 'IMAGE_DIRECTORY' does not exist in the current context Source Error:

Line 84: 
Line 85: if (imgHeight != currentImage.Height | imgWidth != currentImage.Width) {
Line 86: html = "<a href=\"" + IMAGE_DIRECTORY + Path.GetFileName(s) + "\">" + "<img src=\"ShowThumbnail.aspx?img=" + Path.GetFileName(s) + "&w=" + imgWidth + "&h=" + imgHeight + "\" " + "height=\"" + imgHeight + "\" width=\"" + imgWidth + "\" border=1>" + "</a>"; Line 87: } else {
Line 88: 

best regards