如何动态生成WBMP？

%@ Language=VBScript %>
%
Function StoB(varstr)
str2bin = ""
For i = 1 To Len(varstr)
varchar = Mid(varstr, i, 1)
str2bin = str2bin ChrB(AscB(varchar))
Next
StoB = str2bin
End Function
img=chr(0) chr(0) chr(5) chr(2) chr(0) chr(Hf8)

Response.ContentType="image/vnd.wap.wbmp"
Response.BinaryWrite stob(img)
%>