Convert Image into Base64String

//convert image into Base64string
string GetBase64String(string str_imagepathString)
{
string str_image = str_imagepathString;
WebClient wc = new WebClient();
byte[] myimage;
string str_base64 = null;
myimage = wc.DownloadData(str_image);
str_base64 = Convert.ToBase64String(myimage);
return str_base64;
}