[racket] Can't figure out how to send an image with an email

Does anyone know how to send an image with an email? I can't find any 
documentation online. 

I can send the list-of-strings email via the following code just fine:

(require (lib "smtp.ss" "net")
         (lib "dns.ss" "net")
         (lib "mzssl.ss" "openssl")
         (lib "head.ss" "net"))

(smtp-send-message
 (dns-get-address (dns-find-nameserver) "smtp.gmail.com") ; server-string
 "dummy at gmail.com" ; from-string
 '("joe at smoo.com") ; to-list-of-strings
 (standard-message-header 
                          "dummy at gmail.com" 
                          '("joe at smoo.com")  
                          '()                    
                          '()
                          "The subject is..."
)
 `("Howdy, Just testing... "  ) ;; message-list-of-strings/bytes
 #:port-no 465
 #:auth-user "dummy"  ; for gmail don't include the @gmail.com
 #:auth-passwd " abc def ghi jkl " ; gmail special password that bypasses dual 
verification
 #:tcp-connect ssl-connect)

Thanks, 
Dan