$str = [img src=sorqin_2014523174838.jpg] 2013 asdfdfdghhhhhhh[img src=sorqin_2014523174838.jpg]sdgfdgdfghdhgfhjfjghjg;
$str = preg_replace/[imgs+src=.*?]/is, <img src="./upload/$1" width="100px" height="100px"/>, $str;
echo $str;

不太熟悉PHP的正则，如果是在js里的话，可以这样

var str = [img src=sorqin_2014523174838.jpg] 2013 asdfdfdghhhhhhh[img src=sorqin_2014523174838.jpg]sdgfdgdfghdhgfhjfjghjg;
str.replace/[/g, <.replace/]/g, >.replace/src=.+?.jpg/g, $1"./upload/$2" width="100px" height="100px";

可以把上面的代码贴到浏览器的控制台里试一下
PHP中的话，使用PHP里相应的replace方法应该就可以了

$str = [img src=sorqin_2014523174838.jpg] 2013 asdfdfdghhhhhhh[img src=sorqin_2014523174838.jpg]sdgfdgdfghdhgfhjfjghjg; $hack = array/[/, /]/, /src=.+?.jpg/; $replace = array<, >, $1"./upload/$2" width="100px" height="100px"; preg_replace$hack, $replace, $str;