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Plugin comparison: Watermarks

A suitable image for a watermark.
A suitable image for a watermark.

If you’re posting pictures that you want to prevent people from copying and reusing without your permission, you probably want to watermark the larger versions. You’ve probably seen watermarks on stock photo sites — a translucent overlay that makes the image useless for making prints from.

What we’d like from a watermarking plugin:

  • Specify what image to overlay as a watermark.
  • Specify how opaque it is and how it’s positioned.
  • Make it tile or just appear once.
  • Specify which sizes of image you want to protect.
  • Apply watermarks automatically when adding images, or manually to selected images.

My recent search for free watermarking plugins yielded three that are general-purpose:

There are others specific to particular situations, like WooCommerce product catalogs.

You may have noticed only one of these is a live link. The other two plugins are broken at this time, so it was easy to pick a winner. Ultimate Watermark fulfills all the requirements except the ability to tile the watermark, and you can do this yourself by using a large watermark that repeats the image you want to overlay.

Auto-scaled images

When you upload an image to your WordPress media library, WordPress automatically creates scaled-down versions of the image for better performance.

Modern web browsers have the intelligence to receive a list of available scalings of a particular image. They then ask the server for the smallest version that looks good at the size the browser’s going to display it. Smaller dimensions (measured in pixels) result in a smaller file (in bytes), so the page loads faster if the server doesn’t send images that are larger than necessary.

The above is introduction for the point that watermarking plugins let you specify which image scalings need to be watermarked.

Screenshot: Checkbox selection of image sizes to apply watermark to.

You may have a different list of image sizes than are shown above. You need watermarks only on the ones that are high enough resolution to be worth stealing.

WordPress by default generates the sizes “full”, “large”, “medium-large”, “medium”, and “thumbnail”. You can set the maximum dimensions for most of these on the Settings > Media screen of your dashboard. Your theme or plugins may define other sizes — for instance, the Graphene theme calls for the “graphene_slider” size. Generally, you don’t control the dimensions of these. Some setups will also create scaled-up versions of what you upload, for use on “retina” displays.

It would be nice if this list would show what dimensions correspond to each size name. I’ll suggest that to the plugin developers after I finish this post. Meanwhile, the plugin Perfect Images shows the details about each image size name.

Preserving original image

The “full” size is your original. If you apply a watermark to it, it’s not possible to use the “remove watermark” function. Ultimate Watermarks has a warning to this effect after the size selection field in the above screenshot:

Important: checking full size is NOT recommended as it’s the original image. You may need it later – for removing or changing watermark, image sizes regeneration or any other image manipulations. Use it only if you know what you are doing.

Use it only if you know what you’re doing. Hmph. Of course, if you watermark the image at all, you generally want to mark the “full” size, since that’ll be the best quality image, the one most worth stealing.

So check the “full” box, and let’s make sure we do know what we’re doing.

The plugin has an option under “image protection and backup” to back up the original, full size image. This backup is kept in a place where website visitors can’t access it via a URL, so it’s secure. If you ask to remove the watermark, and the “full” image is watermarked, the plugin overwrites your full size with this backup image, then uses it to regenerate any other sizes that have watermarks.

This is the easiest way to make it possible to remove watermarks. The only drawback is that it uses more space on your server, so it may not be a good idea if space is tight.

If you don’t want to store backups of the originals, you can instead upload a fresh copy of the original file from your PC or wherever you keep it. This is, however, a major pain.

The problem is that WordPress doesn’t provide a way to upload an updated copy of an existing image with the same filename. You can add another copy of the image to your library, and it’ll be assigned a new, unique filename. Then you must edit every page, post, gallery, etcetera that refers to the old image, and change it to point to the new version.

Using FTP or the File Manager in your hosting provider’s website management screens, you can sneak around through the back door and replace the file. This only replaces the one size, though, so you would need to use a plugin such as Perfect Images to recreate them.

One “gotcha” with that approach is that the watermarking plugin “remembers” which images are watermarked, to avoid reapplying the watermark to an image that already has one. If you replace the “full” image behind the scenes, the plugin thinks that image is watermarked, but in fact it isn’t, so it will (I believe) refuse to apply a watermark to that image.

Again, if you enable the “backup” option, you won’t have to deal with these complexities.

Editing watermarked images

WordPress Media Library has the ability to edit images in your library — you can crop, rotate, flip, and scale them. These edits happen on the original “full” size image, and when you save changes, WordPress also regenerates all the different-sized versions of that image.

If your “full” image has a watermark on it, it’s part of the image, so the watermark will also appear on all the resized versions, including the thumbnail. Generally, this isn’t what you want. So to edit images within WordPress, either do it before applying a watermark, or remove the watermark, then edit, then replace the watermark. Watermark removal can be done if you’ve enabled the backup option as described above.

Or, better yet, do your editing on your own PC before uploading the image in the first place. That way the copy on your website matches the original on your PC.

Other “image protection” features

Ultimate Watermarks and the similar plugins, also provide features to further protect images from theft by making it harder to copy them. In particular, there are options to “Disable right mouse click on images” and “Prevent drag and drop”, two easy ways to grab images off a webpage.

I don’t care for this myself. These restrictions are fairly easy to work around (for instance, there are numerous browser extensions to save all or selected images from a webpage). So they don’t do much to stop thievery by someone who’s even a little determined. But they do make it harder for honest users to do legitimate things, such as opening the image in a new window because it’s too tiny to see and you want to zoom in. I choose to rely on the watermarks.


* Or the free alternative, Gimp.

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