pass a value through different pages

hello
i have a project where i will display pictures to every category.
i need to make an edit option along each picture
i made a link for the edit but i need to pass the id of the picture in order to update it
i have the following code for the display including edit
string pics_table = "<table>";
while (cmdReader.Read())
{
pics_table += "<tr>";
pics_table += "<td>";
pics_table += "<img src='" + pic_location + cmdReader["url"].ToString() + " />";
pics_table += "</td>";
pics_table += "<td width='20px'>";
pics_table += "<a href=editpictures.aspx?picture_id={0}>Edit</a>";
pics_table += "</td>";
pics_table += "</tr>";
}
pics_table += "</table>";
 but the code have something wrong when i pass the picture id to another page. The ID is always being 0
your help is appreciated
than ...