Validation of file uploads in c#

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C#

VS2010

validation

image

, +

Hello, how do i validate the file types that are uploaded ? i only want to allow people to upload their image file types only.

Below is a snippet of code that i use to allow users to upload their file:

private void StartUpLoad()
{
string companyID = this.Label1.Text;

string imgName = FileUpload1.FileName;

string imgPath = "~/Uploads/" + imgName;

int imgSize = FileUpload1.PostedFile.ContentLength;

if (FileUpload1.PostedFile != null && FileUpload1.PostedFile.FileName != "")
{

if (FileUpload1.PostedFile.ContentLength > 1000000)
{
Page.ClientScript.RegisterClientScriptBlock(typeof(Page), "Alert", "alert('File is too big.')", true);
}
else
{

FileUpload1.SaveAs(Server.MapPath(imgPath));
Image1.ImageUrl = imgPath;
Page.ClientScript.RegisterClientScriptBlock(typeof(Page),"Alert","alert('Image saved!')", true);

byte[] theImage = new byte[FileUpload1.PostedFile.ContentLength];
HttpPostedFile Image = FileUpload1.PostedFile;
Image.InputStream.Read(theImage,0(int)FileUpload1.PostedFile.ContentLength);

int length = theImage.Length;
string fileName = FileUpload1.FileName.ToString();
string type = FileUpload1.PostedFile.ContentType;

int size = FileUpload1.PostedFile.ContentLength;
if (FileUpload1.PostedFile != null && FileUpload1.PostedFile.FileName != "")
{

WP_advBLL canwork = new WP_advBLL();
canwork.ExecuteInsert(theImage, type, size, fileName, length,companyID);
Response.Write("File has been uploaded successfully!");
}
}

}

Any idea how to add on to check for type of files selected?