The verification code image generated by php is not displayed.

Today, when I was working on a php verification code program, I found that the generated image was not displayed. I thought it was because the php gd library was not opened. I checked it with phpinfo, the following small series will introduce the solution to this problem.

After the bom is cleared, the code is written at the beginning, and the gd library is also enabled. From here, it is estimated that it is not a problem with the gd library, but it may be in the code of the program.

Code for generating the verification code:

The Code is as follows:

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<? Php /* * Verification Code Generation Program */ $ Letter = ''; // Obtain random numbers For ($ I = 0; $ I <2; $ I ++ ){ $ Letter. = chr (mt_rand (48, 57 )); } // Obtain random letters For ($ I = 0; $ I <2; $ I ++ ){ $ Letter. = chr (mt_rand (65,90 )); } // Reconstruct the Character Sequence $ Strs = str_split ($ letter ); Shuffle ($ strs ); $ Rndstring = ""; While (list (, $ str) = each ($ strs )){ $ Rndstring. = $ str; } // If GD is supported, draw If (function_exists ("imagecreate ")) { // Write cookie to the browser Setcookie ("zjs_ckstr", md5 (strtolower ($ rndstring), time () + 300, '/'); // The verification code is valid for 5 minutes $ Rndcodelen = strlen ($ rndstring ); // Image size $ Im = imagecreate (100,30 ); // $ Im = imagecreatefromgif ("code.gif "); // Font $ Font_type = dirname (_ FILE _). "/data/font/AvantGardeBookBT. ttf "; // Background color $ Backcolor = imagecolorallocate ($ im, 255,255,255 ); // Font color // Imagettftext is not supported $ FontColor = ImageColorAllocate ($ im, 0, 0 ); // Supports imagettftext $ FontColor2 = ImageColorAllocate ($ im, 0, 0 ); // Shadow $ FontColor1 = ImageColorAllocate ($ im, 255,255, 25 ); // Add background noise $ PixColor = imagecolorallocate ($ im, 199,199,199); // miscellaneous color For ($ j = 0; $ j <1000; $ j ++ ){ Imagesetpixel ($ im, rand (0,100), rand (0, 30), $ pixColor ); } // Add a background line For ($ j = 0; $ j <= 3; $ j ++ ){ // Background line color $ LineColor1 = ImageColorAllocate ($ im, rand (0,255), rand (0,255), rand (0,255 )); // Size of the background line direction Imageline ($ im, rand (), $ lineColor1 ); } $ Strposs = array (); // Text For ($ I = 0; $ I <$ rndcodelen; $ I ++ ){ If (function_exists ("imagettftext ")){ $ Strposs [$ I] [0] = $ I * 16 + 17; // X axis $ Strposs [$ I] [1] = mt_rand (20, 23); // y axis Imagettftext ($ im, 5, 5, $ strposs [$ I] [0] + 1, $ strposs [$ I] [1] + 1, $ fontColor1, $ font_type, $ rndstring [$ I]); } Else { Imagestring ($ im, 5, $ I * 16 + 7, mt_rand (2, 4), $ rndstring [$ I], $ fontColor ); } } // Text For ($ I = 0; $ I <$ rndcodelen; $ I ++ ){ If (function_exists ("imagettftext ")){ Imagettftext ($ im, 16, 5, $ strposs [$ I] [0]-1, $ strposs [$ I] [1]-1, $ fontColor2, $ font_type, $ rndstring [$ I]); } } Header ("Pragma: no-cachern "); Header ("Cache-Control: no-cachern "); Header ("Expires: 0rn "); // Output a specific image format with a priority of gif-> jpg If (function_exists ("imagegif ")){ Header ("content-type: image/gifrn "); Imagegif ($ im ); } Else { Header ("content-type: image/policrn "); Imagejpeg ($ im ); } ImageDestroy ($ im ); } ?>

I felt that there was no problem. Later, Baidu found that a high person said that the key was to join ob_clean, which gave me the reason.

Solution

Ob_clean (); // key code to prevent the problem that 'images cannot be displayed due to their own mistakes.

Before adding the header to the output

The Code is as follows:	Copy code
Header ('content-Type: image/png ');