为何验证码不一样？

youxia

南开大学的验证码
6e7a62eb3fbdaf7fe25c266f9379d988  SU900.001.iso
2d71bcfa4389f9583d6d6c0500b886a6  SU900.002.iso
23add015d6054e7179dc377875518025  SU900.003.iso
ba235a1736800792fd17e240a887a65a  SU900.004.iso
2a9a6304c8120dcafecda1c5ee776f05  SU900.005.iso

清华大学的验证码
8f040488644692b707b78a9f5ded8a03  susel90a.iso
2d71bcfa4389f9583d6d6c0500b886a6  susel90b.iso
23add015d6054e7179dc377875518025  susel90c.iso
ba235a1736800792fd17e240a887a65a  susel90d.iso
8d1b47aefd5721df3bc65d61ea179cd9  susel90e.iso

dukyluo

又不是SuSe的发行版，都是自己做的吧