public void DumpImage(string strImgSize, string archiveDir = null, string fileName = null)
{
ImageSize imgSize = ImageSize.stringToSize(strImgSize);
if (privateimgList.Exists(img => img.imgSize == imgSize))
DumpImageData(privateimgList.Find(img => img.imgSize == imgSize), archiveDir, fileName);
else
throw new FileNotFoundException("Image with resolution " + imgSize + " not found");
}