IF condition in where clause

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ASP.NET

SQL

SQL-Server-2008R2

Hello Coders,
I need your help in writing one sql query, i know we can not use directly IF condition in where clause so tell me its alternative.
My scenario is i am doing filter work by using 3 dropdowns and 1 checkbox. Till 3 dropdowns i am able to filter data correctly, now by using checkbox i have to filter my result.
I have product list and i want if user check the checkbox then my result show those records which have atleast one image. Every product have 5 fields for images and i want if any field have value then it should be show otherwise it doesn't include in my result.

<asp:CheckBox ID="chk_image" runat="server" oncheckedchanged="chk_image_CheckedChanged" /> Exclude Without Image Ads

protected void chk_image_CheckedChanged(object sender, EventArgs e)
    {
        Refine_BindRepeaterData();
    }

protected int Refine_BindRepeaterData()
    {
        con.Open();
        SqlCommand cmd = new SqlCommand("sps_searchresult", con);
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue("@country", 1);
        cmd.Parameters.AddWithValue("@state", dd_state.SelectedValue);
        cmd.Parameters.AddWithValue("@pincode", txt_pincode.Text);
        cmd.Parameters.AddWithValue("@category", dd_category.SelectedValue);
        cmd.Parameters.AddWithValue("@subcategory", dd_subcategory.SelectedValue);
        cmd.Parameters.AddWithValue("@OrderBy", dd_sort.SelectedValue);
        //cmd.Parameters.AddWithValue("@iam", dd_postedby.SelectedValue);
        string iam = dd_postedby.SelectedValue;
        if (iam == "All")
        {
            cmd.Parameters.AddWithValue("@iam", DBNull.Value);
        }
        else
        {
            cmd.Parameters.AddWithValue("@iam", dd_postedby.SelectedValue);
        }
        cmd.Parameters.AddWithValue("@image", chk_image.Checked);
        con.Close();
}

ALTER PROCEDURE [dbo].[sps_searchresult]
	@country int,
	@state nvarchar(20),
	@pincode nvarchar(10),
	@category int,
	@subcategory nvarchar(25),
	@OrderBy nvarchar(50),
	@iam nvarchar(50),
	@chkimage bit
	
AS
BEGIN
	
	if(@state='--Select State--' and @pincode='Pincode' and @subcategory='--Select Sub-Category--')
	begin
	select r.*, s.s_name, c.category_name, sc.subcategory_name, CASE iam WHEN 1 THEN 'Professional/Business' ELSE 'Individual' End as iamdetail, substring(description,1,250) AS shortdescription, substring(title,1,30) AS shorttitle, substring(address,1,80) AS shortaddress from tbl_adregister r INNER JOIN tbl_state s ON r.state = s.s_id join tbl_category as c on r.category=c.category_id INNER JOIN tbl_adsubcategory sc on r.ad_id=sc.ad_id 
	where country=@country and category=@category and iam = ISNULL(@iam, iam) and 
	@chkimage=false
		(imagepath1!='' or imagepath2!='' or imagepath3!='' or imagepath4!='' or imagepath5!='')
	
	
	end
end

in where i have to check @chkimage value if it is true then filter result by excluding ad without image and if it is false then result must not be affected(means it should not consider this parameter, just like previous one do : iam = ISNULL(@iam, iam))