What are some best practices for handling user input, such as filtering and validating, before using it in image manipulation functions in PHP?

When handling user input for image manipulation functions in PHP, it is crucial to filter and validate the input to prevent security vulnerabilities such as code injection. One common practice is to use functions like `filter_var()` to sanitize input and `preg_match()` to validate against specific patterns. Additionally, it is recommended to limit the types of files that can be uploaded and check file sizes to prevent potential attacks.

// Example of filtering and validating user input for image manipulation functions

// Filter and validate user input
$imageUrl = filter_var($_POST['image_url'], FILTER_VALIDATE_URL);
if (!$imageUrl) {
    // Handle invalid input error
}

// Check if the file exists and is an image
if (getimagesize($imageUrl) === false) {
    // Handle invalid image error
}

// Perform image manipulation functions using $imageUrl