当然可以,不过新版本的不支持GIF文件的写(读取支持),可以生成JPG格式的缩略图
下面是个比较好的例子,自己看看
<?$FILENAME="image_name";// 生成图片的宽度
$RESIZEWIDTH=400;// 生成图片的高度
$RESIZEHEIGHT=400;
function ResizeImage($im,$maxwidth,$maxheight,$name){
    $width = imagesx($im);
    $height = imagesy($im);
    if(($maxwidth && $width > $maxwidth) || ($maxheight && $height > $maxheight)){
        if($maxwidth && $width > $maxwidth){
            $widthratio = $maxwidth/$width;
            $RESIZEWIDTH=true;
        }
        if($maxheight && $height > $maxheight){
            $heightratio = $maxheight/$height;
            $RESIZEHEIGHT=true;
        }
        if($RESIZEWIDTH && $RESIZEHEIGHT){
            if($widthratio < $heightratio){
                $ratio = $widthratio;
            }else{
                $ratio = $heightratio;
            }
        }elseif($RESIZEWIDTH){
            $ratio = $widthratio;
        }elseif($RESIZEHEIGHT){
            $ratio = $heightratio;
        }
        $newwidth = $width * $ratio;
        $newheight = $height * $ratio;
        if(function_exists("imagecopyresampled")){
              $newim = imagecreatetruecolor($newwidth, $newheight);
              imagecopyresampled($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
        }else{
            $newim = imagecreate($newwidth, $newheight);
              imagecopyresized($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
        }
        ImageJpeg ($newim,$name . ".jpg");
        ImageDestroy ($newim);
    }else{
        ImageJpeg ($im,$name . ".jpg");
    }
}if($_FILES['image']['size']){
    if($_FILES['image']['type'] == "image/pjpeg"){
        $im = imagecreatefromjpeg($_FILES['image']['tmp_name']);
    }elseif($_FILES['image']['type'] == "image/x-png"){
        $im = imagecreatefrompng($_FILES['image']['tmp_name']);
    }elseif($_FILES['image']['type'] == "image/gif"){
        $im = imagecreatefromgif($_FILES['image']['tmp_name']);
    }
    if($im){
        if(file_exists("$FILENAME.jpg")){
            unlink("$FILENAME.jpg");
        }
        ResizeImage($im,$RESIZEWIDTH,$RESIZEHEIGHT,$FILENAME);
        ImageDestroy ($im);
    }
}?><img src="<? echo($FILENAME.".jpg?reload=".rand(0,999999)); ?>"><br><br><form enctype="multipart/form-data" method="post">
<br>
<input type="file" name="image" size="50" value="浏览"><p>
<input type="submit" value="上传图片">
</form> </body>
</html>