step1: Add Fileupload tag in your .aspx page:
<asp:fileupload id="FileUpload1" runat="server" xmlns:asp="#unknown" />
Step2: Now add a button for saving uploaded file
<asp:button id="Button1" runat="server" onclick="Button1_Click" text="Upload" xmlns:asp="#unknown" />
Step3: Add a folder named "Images" in your project
step4: The C# code for image upload is as follows
protected void Button1_Click(Onject sender, EventArgs e)
{
string FileName = Path.GetFileName(FileUpload1.PostedFile.FileName);
string path = Server.MapPath("/Images"+FileName);
FileUpload1.SaveAs(path);
}