What best practices should PHP developers follow when implementing caching mechanisms in scripts that generate and serve images, like Captchas, to avoid discrepancies between saved and displayed images?

When implementing caching mechanisms for scripts that generate and serve images like Captchas, PHP developers should ensure that the caching mechanism takes into account the unique characteristics of each image being generated. One way to avoid discrepancies between saved and displayed images is to use a cache key that incorporates the parameters used to generate the image. By doing so, the caching mechanism can correctly identify and retrieve the cached image based on the input parameters, ensuring consistency between saved and displayed images. 

// Generate a unique cache key based on input parameters
$cacheKey = 'captcha_' . md5($captchaText . $captchaWidth . $captchaHeight);

// Check if the cached image exists
if (apcu_exists($cacheKey)) {
    // Serve the cached image
    header('Content-Type: image/png');
    echo apcu_fetch($cacheKey);
} else {
    // Generate the new image
    $image = generateCaptchaImage($captchaText, $captchaWidth, $captchaHeight);

    // Cache the generated image
    apcu_store($cacheKey, $image);
    
    // Serve the newly generated image
    header('Content-Type: image/png');
    echo $image;
}

Keywords

image caching PHP scripts Captchas discrepancies saved images

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