Php simple verification code generation instance

The verification code can prevent some users from repeatedly submitting the code to guess the password or use brute force tools to guess the password. After the verification code is added, it makes them more difficult, next I will provide a session-based verification code program.

Verification codes are often used during website login and registration to prevent others from using mechanical brute force registration or login. In addition, the verification code can ensure the website security to a certain extent, the following is a simple verification code generation and a value is assigned to the session.

The Code is as follows:

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<? Php Session_start (); Header ("Content-type: image/png "); // Create white paper with true color $ Im = @ imagecreatetruecolor (50, 20) or die ("image creation failed "); // Obtain the background color $ Background_color = imagecolorallocate ($ instant, 255,255,255 ); // Fill in the background color (this is similar to a barrel) Imagefill ($ im, 0, 0, $ background_color ); // Obtain the border color $ Border_color = imagecolorallocate ($ im, 200,200,200 ); // Draw a rectangle with a border color of 200,200,200 Imagerectangle ($ im, $ border_color ); // Show off the background line by line. Use 1 or 0 in full screen. For ($ I = 2; $ I <18; $ I ++ ){ // Obtain random light colors $ Line_color = imagecolorallocate ($ im, rand (200,255), rand (200,255), rand (200,255 )); // Draw a line Imageline ($ im, 2, $ I, 47, $ I, $ line_color ); } // Set the font size $ Font_size = 12; // Set the printed text $ Str [0] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ "; $ Str [1] = "abcdefghijklmnopqrstuvwxyz "; $ Str [2] = 01234567891234567890123456 ″; // Obtain 1st random texts $ Imstr [0] ["s"] = $ Str [rand (0, 2)] [rand (0, 25)]; $ Imstr [0] ["x"] = rand (2, 5 ); $ Imstr [0] ["y"] = rand (1, 4 ); // Obtain 2nd random texts $ Imstr [1] ["s"] = $ Str [rand (0, 2)] [rand (0, 25)]; $ Imstr [1] ["x"] = $ imstr [0] ["x"] + $ font_size-1 + rand ); $ Imstr [1] ["y"] = rand (1, 3 ); // Obtain 3rd random texts $ Imstr [2] ["s"] = $ Str [rand (0, 2)] [rand (0, 25)]; $ Imstr [2] ["x"] = $ imstr [1] ["x"] + $ font_size-1 + rand ); $ Imstr [2] ["y"] = rand (1, 4 ); // Obtain 4th random texts $ Imstr [3] ["s"] = $ Str [rand (0, 2)] [rand (0, 25)]; $ Imstr [3] ["x"] = $ imstr [2] ["x"] + $ font_size-1 + rand ); $ Imstr [3] ["y"] = rand (1, 3 ); // Assign the displayed array to the session $ _ SESSION ['code'] = $ imstr [0] ["s"]. $ imstr [1] ["s"]. $ imstr [2] ["s"]. $ imstr [3] ["s"]; // Write random strings 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 ); } // Display the image Imagepng ($ im ); // Destroy the image Imagedestroy ($ im ); ?>