Issue related sending emails in asp.net

Hi Every1,
Problem:== i m able to send the mail to everyone,but without background image ..if i send a mail to my id on my pc, i m getting the backgroung image but on other pc they cannot get the image..

               i made a small application through we can send happy bithday emails to employee, to celebrate Birthday.
[Code Below][Code below contains background image and message to display]

private string GetEmailMessage()
    {
        string name = string.Empty;
        string occassion = string.Empty;
        string time = string.Empty;
        string amount = string.Empty;
        StringBuilder sb = new StringBuilder(string.Empty);
    ...