确保图片上传安全：如何验证上传的文件是否为正版图片

import java.io.ioexception;
import java.nio.file.files;
import java.nio.file.path;

public boolean isvalidimagefile(path filepath) throws ioexception {
    string mimetype = files.probecontenttype(filepath);
    return mimetype != null && (mimetype.equals("image/jpeg") || mimetype.equals("image/png") || mimetype.equals("image/gif"));
}

package main

import (
    "mime/multipart"
    "net/http"
)

func isvalidimagefile(file multipart.file) bool {
    buffer := make([]byte, 512)
    _, err := file.read(buffer)
    if err != nil {
        return false
    }

    mimetype := http.detectcontenttype(buffer)
    return mimetype == "image/jpeg" || mimetype == "image/png" || mimetype == "image/gif"
}

function isvalidimagefile($filepath) {
    $mimetype = mime_content_type($filepath);
    return in_array($mimetype, ['image/jpeg', 'image/png', 'image/gif']);
}

// usage example
if (isvalidimagefile($_files['uploaded_file']['tmp_name'])) {
    // process the image file
}

const fs = require('fs');
const filetype = require('file-type');

async function isvalidimagefile(filepath) {
    const buffer = await fs.promises.readfile(filepath);
    const type = await filetype.frombuffer(buffer);

    return type && ['image/jpeg', 'image/png', 'image/gif'].includes(type.mime);
}

// example usage
isvalidimagefile('path/to/file').then(isvalid => {
    console.log(isvalid ? 'valid image' : 'invalid image');
});

import magic

def is_valid_image_file(file_path):
    mime_type = magic.from_file(file_path, mime=True)
    return mime_type in ['image/jpeg', 'image/png', 'image/gif']

# Example usage
print(is_valid_image_file('path/to/file'))