上传文件图像验证

在有人可以上传图像之前，我有这些代码作为我的验证。然而，当我尝试上传不同的文件，如视频文件等，它仍然通过?我遗漏了什么?这是我的全部代码。对不起，我不知道你在找什么。它只是接受我上传的所有东西，它上传了照片，但是没有图片。

protected void Page_Load(object sender, EventArgs e)
    {
        if (Session["IslandGasAdminPM"] != null)
        {
            if (!IsPostBack)
            {
                GetCategories();
                AddSubmitEvent();
            }
            if (Request.QueryString["alert"] == "success")
            {
                Response.Write("<script>alert('Record saved successfully')</script>");
            }
        }
        else
        {
            Response.Redirect("LogIn.aspx");
        }
    }
    private void AddSubmitEvent()
    {
        UpdatePanel updatePanel = Page.Master.FindControl("AdminUpdatePanel") as UpdatePanel;
        UpdatePanelControlTrigger trigger = new PostBackTrigger();
        trigger.ControlID = btnSubmit.UniqueID;
        updatePanel.Triggers.Add(trigger);
    }
    private void GetCategories()
    {
        ShoppingCart k = new ShoppingCart();
        DataTable dt = k.GetCategories();
        if (dt.Rows.Count > 0)
        {
            ddlCategory.DataValueField = "CategoryID";
            ddlCategory.DataTextField = "CategoryName";
            ddlCategory.DataSource = dt;
            ddlCategory.DataBind();
        }
    }
    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
    }
    protected void btnSubmit_Click(object sender, EventArgs e)
    {
        if (uploadProductPhoto.PostedFile != null)
        {
            SaveProductPhoto();
            ShoppingCart k = new ShoppingCart()
            {
                ProductName = txtProductName.Text,
                ProductImage = "~/ProductImages/" + uploadProductPhoto.FileName,
                ProductPrice = txtProductPrice.Text,
                ProductDescription = txtProductDescription.Text,
                CategoryID = Convert.ToInt32(ddlCategory.SelectedValue),
                TotalProducts = Convert.ToInt32(txtProductQuantity.Text)
            };
            k.AddNewProduct();
            ClearText();
            Response.Redirect("/Admin/AddNewProduct.aspx?alert=success");
        }
        else
        {
            Response.Write("<script>alert('Please upload photo');</script>");
        }
    }
    private void ClearText()
    {
        uploadProductPhoto = null;
        txtProductName.Text = String.Empty;
        txtProductPrice.Text = String.Empty;
        txtProductDescription.Text = String.Empty;
        txtProductQuantity.Text = String.Empty;
    }
    private void SaveProductPhoto()
    {
        if (uploadProductPhoto.PostedFile != null)
        {
            string filename = uploadProductPhoto.PostedFile.FileName.ToString();
            string fileExt = System.IO.Path.GetExtension(uploadProductPhoto.FileName);
            //check filename length
            if (filename.Length > 96)
            {
                Response.Write("Image should not exceed 96 characters");
            }
            //check file type
            else if (fileExt != ".jpg" && fileExt != ".jpeg" && fileExt != ".png" && fileExt != ".bmp")
            {
                Response.Write("Only jpg,jpeg,bmp and png are allowed");
            }
            //check file size
            else if (uploadProductPhoto.PostedFile.ContentLength > 4000000)
            {
                Response.Write("Image should not exceed 4MB");
            }
            //Save images to folder
            else
            {
                uploadProductPhoto.SaveAs(Server.MapPath("~/ProductImages/" + filename));
            }
        }