Easy Watermarking with ImageMagick

Dave Taylor — Wed, 29 Oct 2014 20:02:58 +0000

Let's start with some homework. Go to Google (or Bing) and search for "privacy is dead, get over it". I first heard this from Bill Joy, cofounder of Sun Microsystems, but it's attributed to a number of tech folk, and there's an element of truth to it. Put something on-line and it's in the wild, however much you'd prefer to keep it under control.

Don't believe it? Ask musicians or book authors or film-makers. Now, whether the people who would download a 350-page PDF instead of paying $14 for a print book are hurting sales, that's another question entirely, but the Internet is public and open, even the parts that we wish were not.

This means if you're a photographer or upload images you'd like to protect or control, you have a difficult task ahead of you. Yes, you can add some code to your Web pages that makes it impossible to right-click to save the image, but it's impossible to shut down theft of intellectual property completely in the on-line world.

This is why a lot of professional photographers don't post images on-line that are bigger than low-resolution thumbnails. You can imagine that wedding photographers who make their money from selling prints (not shooting the wedding) pay very close attention to this sort of thing!

Just as people have learned to accept poor video in the interest of candor and funny content thanks to YouTube, so have people also learned to accept low-res images for free rather than paying even a nominal fee for license rights and a high-res version of the photograph or other artwork.

There is another way, however, that's demonstrated by the stock photography companies on-line: watermarking.

You've no doubt seen photos with embedded copyright notices, Web site addresses or other content that mars the image but makes it considerably harder to separate it from its original source.

It turns out that our friend ImageMagick is terrific at creating these watermarks in a variety of different ways, and that's what I explore in this column. It's an issue for a lot of content producers, and I know the photos I upload constantly are being ripped off and reused on other sites without permission and without acknowledgement.

To do this, the basic idea is to create a watermark-only file and then blend that with the original image to create a new one. Fortunately, creating the new image can be done programmatically with the convert program included as part of ImageMagick.

Having said that, it's really mind-numbingly complex, so I'm going to start with a fairly uninspired but quick way to add a watermark using the label: feature. In a nutshell, you specify what text you want, where you want it on the image, the input image filename and the output image filename. Let's start with an image (Figure 1).

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Image Manipulation with ImageMagick

Dave Taylor — Thu, 17 Apr 2014 17:46:10 +0000

by Dave Taylor

I've spent a lot of time in my column talking about text processing and analysis, with the basic assumption that if you're using the command line, you're focused on text. That's not always true, and if you work with images at all—whether JPEG, PNG, GIF or another format—there's a free-to-download suite of image-related utilities available that offers rather amazing capabilities direct from the command line and, therefore, also from within shell scripts.

I'm talking about ImageMagick, a set of programs that has grown and expanded through the years and now includes powerful Perl and Ruby interfaces too. But, pshaw! We don't need no stinkin' Perl or Ruby. We'll stick with our hard-core shell commands, thank you very much.

You'll find a downloadable binary and source both at http://www.imagemagick.org, and as always, I recommend you download source and compile it on your system if you can. It's far more reliable than hoping someone else's compiled version is optimized for your own hardware configuration.

A variety of different commands are included with the ImageMagick distribution that I divide into "analysis" and "editing" tools. For this article, let's stick with the analysis tools. Let me start by showing you how much more information it offers on a typical image file than the standard Linux command line.

Analyzing Images for Non-Optimized Resolutions

If you've been using Linux for even a short time, you've probably learned about the file command. It can be helpful with some file types:


$ file wp-content.tar.gz
wp-content.tar.gz: gzip compressed data, from Unix

But, the command is generally useless with images:


$ file pvp.jpg
pvp.jpg: JPEG image data, EXIF standard

Um, what about image size? How about any useful info at all? Jeez.

Enter the ImageMagick identify command:


$ identify pvp.jpg
pvp.jpg JPEG 970x311 DirectClass 114kb 0.010u 0:01

Ahh...so this particular image has the dimensions (the suite refers to dimensions as the "geometry" of the image) of 970x311. That's useful.

Do you want even more information though? The -verbose option spits out a somewhat overwhelming amount of data:

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