PHP Simple Verification Code Generation Example _php tutorial

Verification code can prevent some users repeatedly submit to guess the password or the use of brute force tools to guess the password, we added a verification code after they added a lot of difficulty, below I provide a program based on the session verification code.

In the site's landing and registration, often use the verification code to prevent others with mechanical violence registration or landing, plus verification code to a certain extent to make the site a lot of security, the following is a relatively simple verification code generation, at the same time to assign values to the session.

The code is as follows

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Session_Start (); Header ("Content-type:image/png"); Create True Color white paper $im = @imagecreatetruecolor (a) or Die ("Build image Failed"); Get background color $background _color = imagecolorallocate ($im, 255, 255, 255); Fill the background color (this thing is like oil barrels) Imagefill ($im, 0,0, $background _color); Get border color $border _color = imagecolorallocate ($im, 200,200,200); Draw a rectangle, border color 200,200,200 Imagerectangle ($im, 0,0,49,19, $border _color); Line up background, full screen with 1 or 0 for ($i =2; $i <18; $i + +) { Get random tint $line _color = Imagecolorallocate ($im, Rand (200,255), Rand (200,255), Rand (200,255)); Draw Line Imageline ($im, 2, $i, $i, $line _color); } Set Font size $font _size=12; Set up the printed text $Str [0] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; $STR [1] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; $STR [2] = "01234567891234567890123456″; Get a 1th random text $imstr [0]["s"] = $Str [rand (0,2)][rand (0,25)]; $IMSTR [0]["x"] = rand (2,5); $imstr [0]["y"] = rand (1,4); Get a 2nd random text $imstr [1]["s"] = $Str [rand (0,2)][rand (0,25)]; $IMSTR [1]["x"] = $imstr [0]["x"]+ $font _size-1+rand (0,1); $imstr [1]["y"] = rand (1,3); Get a 3rd random text $imstr [2]["s"] = $Str [rand (0,2)][rand (0,25)]; $IMSTR [2]["x"] = $imstr [1]["x"]+ $font _size-1+rand (0,1); $imstr [2]["y"] = rand (1,4); Get a 4th random text $imstr [3]["s"] = $Str [rand (0,2)][rand (0,25)]; $IMSTR [3]["x"] = $imstr [2]["x"]+ $font _size-1+rand (0,1); $imstr [3]["y"] = rand (1,3); Assigns the displayed array to the session $_session[' CODE ' = $imstr [0]["S"]. $imstr [1]["S"]. $imstr [2]["S"]. $imstr [3]["S"]; Write Random string for ($i =0; $i <4; $i + +) { $text _color = Imagecolorallocate ($im, Rand (50,180), Rand (50,180), Rand (50,180)); Imagechar ($im, $font _size, $imstr [$i] ["X"], $imstr [$i] ["Y"], $imstr [$i] ["s"], $text _color); } Show pictures Imagepng ($im); Destroying pictures Imagedestroy ($im); ?>

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