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How to allow `` to accept only image files?

html
client-side-validation
server-side-validation
file-upload
Alex KataevbyAlex Kataev·Sep 28, 2024
TLDR

Immediately restrict <input type="file"> to images with the accept attribute set to image/* or specific extensions like .png, .jpg for targeted formats. For instance:

<input type="file" accept="image/png, image/jpeg">

This marks the first step to limiting your <input> field by filtering to show only the PNG and JPEG images, providing a more streamlined file selection process.

Back to basics: Implementing the <input> element

Client-side filtering: A first line of defense

The HTML accept attribute acts as a lane assistant, guiding users to upload files in the desired format. But remember - this is just client-side filtering.

<!-- Yes sir, only .png, .jpg or .jpeg images shall pass! --> <input type="file" accept=".png, .jpg, .jpeg">

When only pictures are invited to the party: The image/* wildcard

The image/* wildcard accepts any image type, permitting all image formats to pass through this filter.

<!-- All types of images may join the party --> <input type="file" accept="image/*">

For those who believe in second chances: Enhancing file upload with JavaScript

You may also employ JavaScript to perform additional client-side validation for better security. It's like a bouncer who double-checks the ID at the club door.

Server-side validation: The key to secure file uploads

The boss level check: Robust server-side validation

While filters and JavaScript provide a level of security, the true hero is server-side validation. In PHP, you might use getimagesize() or finfo_file() for deeper file validation.

// PHP doesn't always trust HTML and JS, thus, extra check! if(isset($_FILES['file']) && getimagesize($_FILES['file']['tmp_name'])) { // Process the image file }

Dealing with varying browser compatibilities and mobile support

Understanding your audience: Browser compatibility

While coding, ensure your solution works across as many browsers as it can, especially considering some older ones. Consult Can I Use for updated browser compatibility details.

Mobile support: Catering to a mobile-first world

Given the ubiquitous use of mobile devices, remember to test your feature across mobile platforms. Browser support for accept attribute varies across them.

Calling in the cavalry: Checking the compatibility of accept attribute

Note that Internet Explorer 10+, Chrome, Firefox, Safari 6+, and Opera 15+ all support the accept attribute.

Server-end checks: Guarding the fort

Close the loophole by ensuring robust server-side checks. Use PHP's isset() to safeguard before processing the file.