THINKPHP+IIS6.0+WIN2003 Verification code garbled, how to deal with

THINKPHP+IIS6.0+WIN2003 Verification Code garbled

This verification code is not thinkphp, the Web site on the local computer (win8.1) and other win2003 normal display, can be transmitted to server A This error occurs
Server A before has used the DZ forum, 5.2.17 PHP version, how to debug? Ask, thank you.
------to solve the idea----------------------
Lao Xu has said to remove the BOM head if you do not know what is the BOM head Baidu a bit
------to solve the idea----------------------

$s = Base64_decode (' 77u/r0lgoddhmgawakeaan//fwrkzefodqaaacwaaaaamgawaaacloypqsmy/4cctaihmcxa+ mp8x1c1kylayzpyf8mqquyjthyxjbyl65wz2ird0ozuscarng4vs9xmfp6mxvpe+o6jkwmblvkoqojgexabp2ttrqguvrzvhmoyr9n7/ Pvlpcfg5veg15gxfmv0jnl3prhebqgfbzmce9q1eykzsysofco6slpqmtwz4rm4guaaacvwggtraaa7 ');
echo Bin2Hex ($s);

EFBBBF47494638376132001600a10000dfff7d6464644168750000002c00 ...
This EFBBBF is Utf-8 's BOM head.

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