如何在PHP中实现图片上传和处理

<fORM action="upload.php" method="post" enctype="multipart/form-data">
  <input type="file" name="image">
  <input type="submit" value="Upload">
</form>

<?php
$target_dir = "uploads/"; // 上传文件存储的目录
$target_file = $target_dir . basename($_FILES["image"]["name"]);  // 获取上传的文件名
$uploadOk = 1;  // 默认设置上传标识为1，表示上传成功

// 检测上传的文件是不是真实的图片
if(isset($_POST["submit"])) {
    $check = getimagesize($_FILES["image"]["tmp_name"]);
    if($check !== false) {
        echo "File is an image - " . $check["mime"] . ".";
        $uploadOk = 1;
    } else {
        echo "File is not an image.";
        $uploadOk = 0;
    }
}

// 检测文件是否已经存在
if (file_exists($target_file)) {
    echo "Sorry, file already exists.";
    $uploadOk = 0;
}

// 检测文件大小是否超过限制
if ($_FILES["image"]["size"] > 5000000) {
    echo "Sorry, your file is too large.";
    $uploadOk = 0;
}

// 检测上传标识是否为1，如果是，将上传的文件移动到指定目录
if ($uploadOk == 1) {
    if (move_uploaded_file($_FILES["image"]["tmp_name"], $target_file)) {
        echo "The file ". basename( $_FILES["image"]["name"]). " has been uploaded.";
    } else {
        echo "Sorry, there was an error uploading your file.";
    }
}
?>

<?php
// 指定缩略图的宽度和高度
$thumb_width = 200;
$thumb_height = 200;

// 指定原图和缩略图的文件名
$image_file = "uploads/" . basename($_FILES["image"]["name"]);
$thumbnail_file = "thumbnails/" . basename($_FILES["image"]["name"]);

// 创建一个Image对象，用于操作图片
$image_res = new GdImage();
$image_res->load($image_file);

// 获取原图的宽度和高度
$orig_width = $image_res->getWidth();
$orig_height = $image_res->getHeight();

// 计算缩略图的宽度和高度
$ratio_orig = $orig_width / $orig_height;
if ($thumb_width / $thumb_height > $ratio_orig) {
    $thumb_width = $thumb_height * $ratio_orig;
} else {
    $thumb_height = $thumb_width / $ratio_orig;
}

// 创建一个新的Image对象，用于生成缩略图
$thumb_res = imagecreatetruecolor($thumb_width, $thumb_height);

// 将原图缩放到指定大小，并复制到新的图像上
imagecopyresampled($thumb_res, $image_res, 0, 0, 0, 0, $thumb_width, 
$thumb_height, $orig_width, $orig_height);

// 将缩略图保存成一个JPEG文件
imagejpeg($thumb_res, $thumbnail_file);
?>