ProFree rules cover post type and image size. Pro adds file type, image dimensions, file size, orientation, aspect ratio, date range, post category, and (with WooCommerce) product_cat & product_tag.View pricing & buy →

Conditional rules

Most sites don't want every image watermarked. You probably want to:

• Stamp product photos but skip avatars.
• Watermark gallery images but leave thumbnails clean.
• Apply only to images larger than 1000 px.
• Different watermark for product photos than for blog images.

Conditional rules let you do all of that without writing code.

Where rules are configured

Open Watermark → Edit your template → Rules.

You'll see one or more rule rows. Each row is a single condition. Multiple rules within a watermark are AND-combined (all must match).

Click Add rule to add another condition. Click × to remove.

Free rule types

Rule	What it matches
Post type	Apply only when the image is attached to a post of this type (post, page, attachment, custom CPTs).
Image size	Apply only to specific WordPress subsizes (full, large, medium, thumbnail, …).

If you leave Image size empty, every subsize is watermarked (WatermarkHelper.php:660–662).

Pro rule types

PROGranular conditions

Pro adds file type, dimensions, file size, orientation, aspect ratio, date range, and category-based rules. With WooCommerce active, you also get product category and tag rules.

Unlock advanced rules →

Rule	What it matches
File type (file_type)	MIME type — image/jpeg, image/png, image/gif, image/webp. Skip e.g. PNG-with-alpha to avoid black backgrounds.
Image width	Match width as is greater than, is less than, or equals (in px). Skip thumbnails.
Image height	Same operators on height.
File size	Skip very small or very large files. Operators: >, <, = (KB / MB).
Image orientation	Landscape / portrait / square.
Image aspect ratio	Match 16:9, 4:3, 1:1, custom.
Date range	Apply only to images uploaded between two dates.
Post category	Match parent post's category (taxonomy category).
product_cat (WC)	WooCommerce product category.
product_tag (WC)	WooCommerce product tag.

The full list of registered Pro condition types is in ProAdminManager.php:1017–1118.

Operators

Each rule has an operator. Available values:

Operator	Meaning
equals	Exact match.
not_equals	Not this value.
contains	Substring match (string fields).
greater_than	Numeric comparison.
less_than	Numeric comparison.
in	One of a list.
not_in	None of a list.

Common rule recipes

Watermark only large images (≥ 1000 px wide)

Rule	Operator	Value
Image width	greater_than	1000

Watermark only product gallery images

Rule	Operator	Value
Post type	equals	product
Image size	in	full, large

Watermark JPEG and WebP, but skip PNG (transparency)

Rule	Operator	Value
File type	in	image/jpeg, image/webp

Different watermark for blog vs product

Create two templates:

Template A — Blog watermark

Rule	Operator	Value
Post type	equals	post

Template B — Product watermark

Rule	Operator	Value
Post type	equals	product

Each upload runs through both templates; only the matching one applies.

Watermark only photos uploaded after 2024

Rule	Operator	Value
Date range	between	2024-01-01 → today

Empty rules → apply to all

If a watermark has no rules at all, it applies to every uploaded image — subject to the image-size match in watermark_sizes (also acting as apply to all when empty).

Rule precedence vs legacy

Older versions of Ultimate Watermark used watermark_on and watermark_post_types meta directly (WatermarkHelper.php:494–519). The current build prefers unified watermark_rules:

1. If watermark_rules is non-empty → evaluate via RulesEvaluator.
2. If watermark_rules is empty → fall back to legacy watermark_on + sizes (WatermarkHelper.php:726–793).

You don't need to think about this unless you're migrating from a very old install — the new builder writes watermark_rules.

Custom rule types via filter

Add your own condition types by hooking uwm_condition_types (AddWatermarkPage.php:1082):

add_filter( 'uwm_condition_types', function ( $types ) {
    $types['custom_meta'] = [
        'label'     => 'Custom post meta',
        'operators' => [ 'equals', 'not_equals' ],
    ];
    return $types;
} );

add_filter( 'uwm_evaluate_condition', function ( $matches, $rule, $context ) {
    if ( $rule['type'] !== 'custom_meta' ) return $matches;
    $value = get_post_meta( $context['post_id'], $rule['meta_key'], true );
    return $value === $rule['value'];
}, 10, 3 );

See Hooks & filters for the full evaluator API.

Performance note

Each rule is evaluated per subsize during upload / metadata generation. Adding 10 rules per template costs ~10 × N evaluations per upload (where N = number of subsizes). For typical sites this is negligible — but if you're processing thousands of uploads in a batch, prefer fewer specific rules over many generic ones.

Where to go next

• 🖼️ Watermarks — building the templates.
• 📐 Positioning — anchor & offset details.
• ⚡ Performance — batch processing big libraries.
• 💎 Pro features — full advanced rule set.