Code for generating a very good four-digit verification code in ASP-[ASP program]

<%
Call com_creatvalidcode ("validcode ")

Sub com_creatvalidcode (PSN)
'Prohibit caching
Response. expires =-9999
Response. addheader "Pragma", "No-Cache"
Response. addheader "cache-ctrol", "No-Cache"
Response. contenttype = "image/BMP"

Randomize

Dim I, II, III

Const codds = 4' probability of occurrence of miscellaneous
Const camount = 10' text count
Const ccodes = "0123456789"

'Color data (character, background)
Dim vcolordata (1)
Vcolordata (0) = chrb (1) & chrb (52) & chrb (255) 'Blue 1, green 52, red 255 (red)
Vcolordata (1) = chrb (255) & chrb (255) & chrb (255) 'Blue 255, green 255, red 255

'Randomly generated characters
Dim vcode (4), vcodes
For I = 0 to 3
Vcode (I) = int (RND * camount)
Vcodes = vcodes & Mid (cCode, vcode (I) + 1, 1)
Next

'Session ("vcodes") = vcode' record the session
Session ("checkcode") = vcodes 'record the session
'Character data
Dim vnumberdata (35)
Vnumberdata (0) = "1110000111110111101111011110111101001011110100101111010010111101001011110111101111011110111110000111"
Vnumberdata (1) = "1111011111110001111111110111111111011111111101111111110111111111011111111101111111110111111100000111"
Vnumberdata (2) = "1110000111110111101111011110111111111011111111011111111011111111011111111011111111011110111100000011"
Vnumberdata (3) = "1110000111110111101111011110111111110111111100111111111101111111111011110111101111011110111110000111"
Vnumberdata (4) = "1111101111111110111111110011111110101111110110111111011011111100000011111110111111111011111111000011"
Vnumberdata (5) = "1100000011110111111111011111111101000111110011101111111110111111111011110111101111011110111110000111"
Vnumberdata (6) = "1111000111111011101111011111111101111111110100011111001110111101111011110111101111011110111110000111"
Vnumberdata (7) = "1100000011110111011111011101111111101111111110111111110111111111011111111101111111110111111111011111"
Vnumberdata (8) = "1110000111110111101111011110111101111011111000011111101101111101111011110111101111011110111110000111"
Vnumberdata (9) = "1110001111110111011111011110111101111011110111001111100010111111111011111111101111011101111110001111"
'Output image file headers
Response. binarywrite chrb (66) & chrb (77) & chrb (230) & chrb (4) & chrb (0) & chrb (0) & chrb (0) & chrb (0) &_
Chrb (0) & chrb (0) & chrb (54) & chrb (0) & chrb (0) & chrb (0) & chrb (40) & chrb (0) &_
Chrb (0) & chrb (0) & chrb (40) & chrb (0) & chrb (0) & chrb (0) & chrb (10) & chrb (0) &_
Chrb (0) & chrb (0) & chrb (1) & chrb (0)

'Output Image Information Headers
Response. binarywrite chrb (24) & chrb (0) & chrb (0) & chrb (0) & chrb (0) & chrb (0) & chrb( 176) & chrb (4) &_
Chrb (0) & chrb (0) & chrb (18) & chrb (11) & chrb (0) & chrb (0) & chrb (18) & chrb (11) &_
Chrb (0) & chrb (0) & chrb (0) & chrb (0) & chrb (0) & chrb (0) & chrb (0) & chrb (0) &_
Chrb (0) & chrb (0)

For I = 9 to 0 step-1 'goes through all rows
For II = 0 to 3' goes through all words
For IIi = 1 to 10' goes through all pixels
'Output image data row by row, word by word, and pixel by Pixel
If RND * 99 + 1 <codds then' random generation of miscellaneous
Response. binarywrite vcolordata (0)
Else
Response. binarywrite vcolordata (mid (vnumberdata (vcode (II), I * 10 + III, 1 ))
End if
Next
Next
Next

End sub

'The generated verification code is stored in the session, and it is displayed on the to be referenced.

%>