function isImageFile(vFile){
        // if vFile is File or Blob Object
        if((typeof window.File !== "undefined" && vFile instanceof window.File) ||
           (typeof window.Blob !== "undefined" && vFile instanceof window.Blob)){
            return (vFile.type.toLowerCase().indexOf("image/") === 0);
        }

        // if vFile is HTMLElement
        var welFile = $(vFile);
        var oFileList = welFile.prop("files");

        if(oFileList && oFileList.length){
            var bResult = true;

            for(var i = 0, nLength = oFileList.length; i < nLength; i++){
                bResult = bResult && isImageFile(oFileList[i]);
            }

            return bResult;
        }

        // if cannot find MIME type from File object
        // get whether filename ends with extension looks like image file
        // like as .gif, .bmp, .jpg, .jpeg, .png.
        if(typeof welFile.val() === "string"){
            htVar.rxImgExts = htVar.rxImgExts || /\.(gif|bmp|jpg|jpeg|png)$/i;
            return htVar.rxImgExts.test(welFile.val());
        }

        // Unavailable to detect mimeType
        return null;
    }
Get whether the file is image with MIME type, and filename extension.
returns boolean or null if unavailable to determine result

@param {Variant} vFile File object or HTMLElement
@returns {Boolean|Null}