Automatic Image Compression in WordPress Without Plugins

Optimizing image size is a key way to speed up your website.
This tutorial summarizes the guide “Automatic Image Compression in WordPress Without Plugins” from Idtheme.

1. Compress Before Upload

The safest and most universal approach is to compress images before uploading to WordPress.

• Use online services such as:
  • compressjpeg.com for JPEG images.
  • compresspng.com for PNG images.
  • Or other desktop/online image compression tools.
• Compress images before uploading to WordPress.

2. Use Built‑in Server Compression

Some servers provide:

• Image compression modules.
• Or CDN integrations that automatically compress images (e.g., Cloudflare Polish, etc.).

If available:

• Enable the feature in your hosting/CDN panel.

3. Use External Scripts/CLI (Advanced)

If you have server access:

• Use tools like jpegoptim, optipng, etc., to compress images in the uploads folder.

Concept steps:

1. Log in to the server via SSH.
2. Navigate to wp-content/uploads.
3. Run compression commands according to the tool used.

This approach requires SSH access and basic server OS knowledge.

4. Via Custom Code (Recommended)

If you want to compress all JPEG or PNG images, add the following code to your theme’s functions.php file:

function idt_prefix_image_quality( $quality, $image_mime_type ) {
    return 70;
}
add_filter( 'wp_editor_set_quality', 'idt_prefix_image_quality', 10, 2 );

For Jetpack Photon users, use the code below to adjust image quality on Photon:

add_filter( 'jetpack_photon_pre_args', function( $args, $image_url, $scheme ) {
    if ( empty( $args['quality'] ) ) {
         $args['quality'] = 70;
    }
    return $args;
}, 10, 3 );

5. When Do You Need an Image Optimization Plugin?

Although the title says “without plugins,” in some cases:

• If the number of images is very large.
• If you don’t have server access (SSH) or a panel with compression features.

Using an image optimization plugin can be a practical solution. However:

• Choose a lightweight and reputable plugin.
• Avoid installing multiple plugins with the same functionality.

The main focus of this guide:

• Get used to compressing images before upload.
• Leverage server/CDN features before adding new plugins.