Php, verification code Image, garbled

Php, verification code Image, garbled code cannot be found, but a lot of garbled code will appear during preview

Ob_clean ();
Header ("Content-Type: image/png ");
$ Img = @ imagecreatetruecolor (50, 20) or die ("fjhb ");
$ Bg_color = imagecolorallocate ($ img, 255,255,255 );
Imagefill ($ img, 0, 0, $ bg_color );

$ Border_color = imagecolorallocate ($ img, 200,200,200 );
Imagerectangle ($ img, $ border_color );
For ($ I = 2; $ I <18; $ I ++ ){
$ Line_color = imagecolorallocate ($ img, rand (200,255), rand (200,255), rand (200,255 ));
Imageline ($ img, 2, $ I, 47, $ I, $ line_color );
}
$ Font_size = 12;
$ Str [0] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ ";
$ Str [1] = "abcdefghijklmnopqrstuvwxyz ";
$ Str [2] = "01234567891234567890123456 ";

$ Imgstr [0] ["s"] = $ str [rand (0, 2)] [rand (0, 25)];
$ Imgstr [0] ["x"] = rand (2, 5 );
$ Imgstr [0] ["y"] = rand (1, 4 );

$ Imgstr [1] ["s"] = $ str [rand (0, 2)] [rand (0, 25)];
$ Imgstr [1] ["x"] = $ imgstr [0] ["x"] + $ font_size-1 + rand );
$ Imgstr [1] ["y"] = rand (1, 3 );

$ Imgstr [2] ["s"] = $ str [rand (0, 2)] [rand (0, 25)];
$ Imgstr [2] ["x"] = $ imgstr [1] ["x"] + $ font_size-1 + rand );
$ Imgstr [2] ["y"] = rand (1, 4 );

$ Imgstr [3] ["s"] = $ str [rand (0, 2)] [rand (0, 25)];
$ Imgstr [3] ["x"] = $ imgstr [2] ["x"] + $ font_size-1 + rand );
$ Imgstr [3] ["y"] = rand (1, 3 );

For ($ I = 0; $ I <4; $ I ++ ){
$ Text_color = imagecolorallocate ($ img, rand (50,180), rand (50,180), rand (50,180 ));
Imagechar ($ img, $ font_size, $ imgstr [$ I] ["x"], $ imgstr [$ I] ["y"], $ imgstr [$ I] ["s"], $ text_color );
}

Imagepng ($ img );
Imagedestroy ($ img );
?>

Reply to discussion (solution)

Is garbled characters rather than images displayed in the browser?
Close your browser and try again. If not, it should be a header issue.
Image output, it is best to use the UTF-8 character set, because May encounter Chinese output.
And UTF-8, should pay attention to BOM header.

Humorous

Ob_clean (); // clear the buffer content, so that even if there is a BOM header, the image will not be affected.
Header ("Content-Type: image/png"); // declare that the post Content is png image data

So even if the program has non-syntactic errors, it is only a cross, rather than garbled code.

I tested it normally here.

Check whether the BOM header is removed.
Are the gd database and other environments complete?

The main problem is the header problem. Is there any output before the header?

Is it because of file encoding?

Whether or not the lZ Preview is garbled as follows:
This problem occurs because the file encoding is:
Then you need to modify it
The preview effect is as follows:

Last night, no matter how I cleaned up the cache, closed my browser, changed the code, and kept a bunch of garbled characters. Today, my computer started and tested the web page again, so it was inexplicably recovered and I was completely confused, you can only beat your computer and play with me !!!!