why textual captchas are FAIL

there are tons of captcha solvers and sites that break images like here but i have been seeing a rise in math captchas so i wanted to real quick discuss something that i thought was kinda funny. its the idea that simple math problems are difficult for bots to solve. i found math captcha or a text based captcha that i thought would be really easy to solve so i decided i would break the captcha real quick.

basically an image captcha had a "textual riddle" version of the code in its alt tag.

one of the most difficult lines it returned was
(((((??? - 1) - 7) - 8) * 8) - 4) = -76
but i knew it had to be a number from 0 to 9 so i wrote a function to spit this out
if ((((((0 - 1) - 7) - 8) * 8) - 4) = -76) then line = 0
if ((((((1 - 1) - 7) - 8) * 8) - 4) = -76) then line = 1
if ((((((2 - 1) - 7) - 8) * 8) - 4) = -76) then line = 2
if ((((((3 - 1) - 7) - 8) * 8) - 4) = -76) then line = 3
if ((((((4 - 1) - 7) - 8) * 8) - 4) = -76) then line = 4
if ((((((5 - 1) - 7) - 8) * 8) - 4) = -76) then line = 5
if ((((((6 - 1) - 7) - 8) * 8) - 4) = -76) then line = 6
if ((((((7 - 1) - 7) - 8) * 8) - 4) = -76) then line = 7
if ((((((8 - 1) - 7) - 8) * 8) - 4) = -76) then line = 8
if ((((((9 - 1) - 7) - 8) * 8) - 4) = -76) then line = 9
computers are really good at math this takes no time to create and execute this simple vb
code:
function solveMath(phrase)
for i = 0 to 9
solveMath = solveMath & "if (" & replace(phrase,"???",i) & ") then line = " & i & vbcrlf
next
execute solveMath
end function
so now this captcha whose images are actually kind of hard to segment and classify is broken because of 4 lines of vb code

im working on cracking my second image captcha this time the letters aren't fixed with and have a rotation. i plan to use a feed forward back propagation learning neural net so ill let you know how that goes and hopefully get to post again about another captcha ive cracked