KDA Thumbnails

• On-the-fly thumbnail generation with GD or Imagick (auto-detected, or force a specific engine on the settings page).
• Output as JPG, PNG or WebP . Global default format setting applies to all thumbnails, including srcset variants.
• Smart caching with optional organization by post type (each post type gets its own subfolder). The cache folder can be any absolute server path or a subfolder inside wp-content/uploads/ .
• Optional watermark — text or image: Text watermark: custom text, color, opacity, position, and font size (in pixels or as a percentage of the smaller image side so it scales with the thumbnail).
• Google Fonts: pick a font family from a curated list. The TrueType file is downloaded once and cached locally, then reused for every render. A custom local .ttf / .otf path can be used instead.
• Outline (stroke) mode: render the text with a colored outline (configurable width in pixels) for readability on any background.
• Image watermark: overlay a selected Media Library image with configurable opacity.

Shortcode [kdath_thumbnail] and PHP helper functions for theme and plugin developers. kdath_get_thumbnail_srcset( $args, $widths ) + kdath_the_thumbnail_srcset() for responsive srcset. Automatic caching of content images by CSS class (configurable list, applied via the the_content filter). Optional responsive srcset/sizes generation: configure a list of widths, and the rendered <img> tag can include srcset with wp -style width descriptors and an optional sizes attribute. Works for plugin shortcodes/PHP functions, content images, and native WordPress featured images. Optional remote image caching (opt-in, SSRF-protected, with TTL refresh and a max file size limit). Automatic cache size limit : the oldest thumbnails are purged automatically when the quota is exceeded. Lightweight admin page: engine status, cache size, font diagnostics and one-click cache clearing. Global output format setting (JPEG / PNG / WebP) applied to all generated thumbnails, including srcset variants.

Watermark font resolution

When a watermark is rendered the font is resolved in this order:

1. 09The selected Google Font (downloaded once to wp-content/uploads/kda-thumbnails-fonts/<family>.ttf and reused).
2. 10A custom local font file path you provide in the settings.
3. 11If neither is available, the text falls back to the engine’s built-in/best-effort font.

The selected Google Font is downloaded on first use and cached, so the watermark always has a real font to render with (important for Imagick, which otherwise renders nothing when no font is configured). The “Status” panel on the settings page shows the resolved font and whether the Google Font has already been downloaded.

Shortcode

[kdath_thumbnail id="123" width="400" height="300" quality="90" crop="center" format="webp" alt="Photo"]

Shortcode parameters:

• id — Media Library attachment ID (integer).
• src — alternative to id : local file path or URL inside wp-content/uploads/ . Remote URLs are only supported when remote caching is enabled; otherwise use a Media Library ID or local path.
• width — target width in pixels (integer).
• height — target height in pixels (integer).
• quality — JPEG/WebP quality, 1-100 (default: 90 from settings).
• crop — crop mode: top , bottom , left , right , center (default: center ).
• format — output format: jpg , png , webp (default: global “Output format” setting).
• alt — image alt text (string).
• class — extra CSS class(es) for the <img> tag (string).

Shortcode return value: an <img> HTML tag with src , width , height , alt , class , and optional srcset / sizes . On error returns empty string for non-admins, or an HTML comment with the error message for admins.

PHP functions

All functions are available after the plugin is activated.

kdath_get_thumbnail( $args )

Returns the cached thumbnail URL ( string ) or WP_Error on failure.

Example:

$url = kdath_get_thumbnail( array( 'id' => 123, 'width' => 400, 'height' => 300 ) );

kdath_the_thumbnail( $args ) / kdath_the_thumbnail_src( $args )

Echoes the thumbnail URL directly. Same args as kdath_get_thumbnail() .

Example:

kdath_the_thumbnail_src( array( 'id' => 123, 'width' => 400 ) );

kdath_get_thumbnail_img( $args, $attributes )

Returns a complete <img> tag. $attributes is an array of extra HTML attributes ( class , loading , decoding , fetchpriority , style , etc.). When “Responsive srcset” is enabled in settings, srcset and sizes are added automatically unless explicitly passed in $attributes .

Example:

echo kdath_get_thumbnail_img( array( 'id' => 123, 'width' => 400, 'height' => 300 ), array( 'class' => 'my-custom-class', 'loading' => 'lazy' ) );

kdath_the_thumbnail_img( $args, $attributes )

Echoes the <img> tag. Useful inside theme templates.

Example:

kdath_the_thumbnail_img( array( 'src' => '/path/to/image.jpg', 'width' => 800, 'height' => 600, 'crop' => 'center' ), array( 'alt' => 'My photo' ) );

kdath_get_thumbnail_srcset( $args, $widths )

Returns a srcset string (e.g. "url1 300w, url2 768w, url3 1200w" ) or WP_Error . Generates one cached thumbnail per width.

Example:

$srcset = kdath_get_thumbnail_srcset( array( 'id' => 123 ), array( 300, 768, 1200 ) );

kdath_the_thumbnail_srcset( $args, $widths )

Echoes the srcset string.

Example:

kdath_the_thumbnail_srcset( array( 'id' => 123 ), array( 300, 768, 1200 ) );

kdath_get_thumbnail_url_from_meta( $post_id, $meta_key = '' )

Returns the thumbnail URL saved in the custom field configured in settings. Requires a Media Library attachment ID. If $meta_key is omitted, the globally configured field name is used.

Example:

echo kdath_get_thumbnail_url_from_meta( 123 );

kdath_the_thumbnail_url_from_meta( $post_id, $meta_key = '' )

Echoes the URL from the custom field.

Example:

echo kdath_the_thumbnail_url_from_meta( 123 );

KDATH_Thumbnail_Cache::clear_all()

Programmatically clear the entire cache. Useful after bulk imports or when you need to regenerate all thumbnails immediately.

Example:

KDATH_Thumbnail_Cache::clear_all();

Automatic content processing (no code required):

When the plugin is active, it automatically hooks into the_content and post_thumbnail_html . Images in post content that have one of the configured CSS classes (Settings — “Classes for automatic caching”) are replaced with cached thumbnails. Featured images rendered by WordPress (including block themes like Twenty Twenty-Five) are also processed and can include srcset/sizes automatically.

If you prefer to apply this manually, use:

add_filter( 'the_content', function( $content ) { return KDATH_Thumbnail_Content_Processor::process( $content ); } );

This replaces standard <img> tags in post content with optimized thumbnails. Useful when you cannot edit theme templates directly.

Custom field for thumbnail URL

When “Custom field for thumbnail URL” ( kdath_thumbs_url ) is configured in Settings — KDA Thumbnails, the plugin automatically saves the generated thumbnail URL into that post meta key for every Media Library attachment. This is useful if you want to access the URL via get_post_meta() without calling the plugin functions again.

Example:

update_post_meta( 123, 'kdath_thumbs_url', 'https://example.com/wp-content/uploads/kda-thumbnails/kdath_abc123_400x300.jpg' ); // Retrieve later: $url = get_post_meta( 123, 'kdath_thumbs_url', true ); // Or via helper: echo kdath_the_thumbnail_url_from_meta( 123 );

Settings reference

All settings are available under Settings — KDA Thumbnails . No code is required.

General tab:

• Cache folder path — absolute server path, or relative to wp-content/uploads/ (default: /wp-content/uploads/kda-thumbnails/ ). Paths starting with public/ are resolved relative to the web root.
• Cache folder URL — public URL for the cache folder. Required when the path is outside the web root.
• Custom field for thumbnail URL — optional meta key name. When set, the plugin saves each generated thumbnail URL into this field for Media Library attachments.
• Organize cache by post type — saves thumbnails in subfolders per post type.
• Classes for automatic caching — comma-separated CSS classes. Images with these classes in post content are automatically replaced with cached thumbnails.
• Image library — choose GD, Imagick, or Auto.
• Output format — default format for generated thumbnails: JPEG, PNG, or WebP. Applies to all thumbnails, including srcset variants.