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Digital watermarking is the process of possibly irreversibly embedding information into a digital signal. The signal may be audio, pictures or video, for example. If the signal is copied, then the information is also carried in the copy. In visible watermarking, the information is visible in the picture or video. Typically, the information is text or a logo which identifies the owner of the media. [Wikipedia]

 

I decide to go with an offline watermarking first, but you can let any Joomla!® extension watermark picture on the fly using php and .htaccess (at the cost of additional CPU server resources).

 

Why Watermarking pictures?

There is a lot of reasons, among others:

  • To limit images stealing, advanced users will still be able to crop/blur your watermark through!
  • To drive more new users/returning visitors to your site, anybody using your images in a forums may want to visit your site if the watermark can be read (don’t use complex logo, except if you have a well known brand)
  • To advertise your online work,

Attention

The first thing to do is to make a backup of your images! applying a watermarking is a non reversible process, usually this mean for Joomla!® to save your /images/stories directory

You’ll have to decide what size you want your photos to be displayed at and how much space the text or logo will take up. Keep it small enough so as not to ruin the photo.

Create a watermark using GIMP

Download the excellent GIMP if not already done.

Create a new picture with transparent background

watermark.in.gimp.02 

Using the text tool, create a black or white title, you can also import/create an original logo.

watermark.in.gimp

Save the file using a .png or .gif extension, don’t use .jpg as it don’t handle transparency

Result:

watermark 

Prepare your Linux server

My script require you to install ImageMagick

ImageMagick®  is a software suite to create, edit, and compose bitmap images. It can read, convert and write images in a variety of formats (over 100) including DPX, EXR, GIF, JPEG, JPEG-2000, PDF, PhotoCD, PNG, Postscript, SVG, and TIFF. Use ImageMagick to translate, flip, mirror, rotate, scale, shear and transform images, adjust image colors, apply various special effects, or draw text, lines, polygons, ellipses and Bézier curves.

ImageMagick install in OpenSuse

As root run

# zipper in ImageMagick

ImageMagick install in Debian

As root run

# apt-get install ImageMagick

Features

Support dir name and filename space

Support space in path and filename, not so easy as you think. Bash force me to use “” around variables to support space in path and use a while loop instead of a for loop to support space in filename.

Scan you directories

Scan your directories recursively for all pictures starting starting from the current directory (.).

Do not watermark all pictures

I don’t want to apply a watermark to all my pictures, I have decided to check against the size of the images and apply only if a threshold is reach (here all images bigger in width than 1024 pixels). The command identify allow you to retrieve the characteristics of any pictures

geometry=$(identify $each)

return for example

./desktop.jpg JPEG 1024x819 1024x819+0+0 DirectClass 8-bit 94.8613kb

Add a bit of Bash REGEX magic (since 2004 with bash 4.0) to correctly identify picture size

regex="([0-9]*)x([0-9]*)"

and voila! I can now use $height and $width in my function.

Limitations

Do not run the script twice or more

Do not run the script twice or more on same directory/sub directories, or the watermark will get darker and darker. The code do not check if any watermark already exist, and apply the same watermark over and over pictures that reach the threshold.

Installation

The script must be runnable

# chmod u+x watermark.sh

Configuration

open the file watermark.sh

# vi watermark.sh

and change all variables value at the top

Position of the Text Watermark

You can position the text using the following Gravity, possible values are: NorthWest, North, NorthEast, West, Center, East, SouthWest, South, SouthEast.

NorthWest North NorthEast
     
  Center  
     
SouthWest South SouthEast

If the -gravity option is present with NorthEast, East, or SouthEast gravity, it gives the distance leftward from the right edge of the image to the right edge of the cropping region. Similarly, if the -gravity option is present with SouthWest, South, or SouthEast gravity, the distance is measured upward between the bottom edges.

See more details HERE  

The bash script

Source Code

 

 

#!/bin/bash
echo "*******************************************"
echo "* Image Watermarking Script               *"
echo "* By Cedric Walter - www.waltercedric.com *"
echo "* Licence GNU/GPL v3 or later              *"
echo "*******************************************"
echo " "

BASEDIR=.

WATERMARK="/srv/www/vhosts/waltercedric.com/httpdocs/watermark.png"

Below this width no watermark will be apllied
MIN_PIC_HEIGHT=600
MIN_PIC_WIDTH=800

# NorthEast, East, or SouthEast gravity, it gives the distance leftward from the
# right edge of the image to the right edge of the cropping region. # Similarly, if the -gravity option is present with SouthWest, South, or SouthEast
# gravity, the distance is measured upward between the bottom edges. WATERMARK_POSITION=northeast Transparency percentage TRANSPARENCY_PERCENTAGE=15 normal user dont change below #this use bash regular expression capabilities regex="([0-9]*)x([0-9]*)" function applyWatermarkForExtension { find $BASEDIR -type f -name "$1" | while read each do geometry=$(identify "$each") echo $geometry if [[ ${geometry} =~ ${regex} ]]; then echo "$geometry matches" i=1 n=${BASH_REMATCH[*]} width=${BASH_REMATCH[$i]} let i++ height=${BASH_REMATCH[$i]} echo width=$width height=$height if [ $width -gt $MIN_PIC_WIDTH ];then echo "Working on $each ..." composite -gravity $WATERMARK_POSITION -dissolve $TRANSPARENCY_PERCENTAGE $WATERMARK "$each" "$each" 2> /dev/null echo "... Done!" fi fi done } add new pictures extensions here applyWatermarkForExtension "*.jpg" applyWatermarkForExtension "*.gif" applyWatermarkForExtension "*.png" applyWatermarkForExtension "*.jpeg" exit 0

Download

Download from my download section.

references