It’s interesting and fairly simple to add/embed a watermark over an image using Java graphics API. The steps are as follows:

• Read the source image file into a BufferedImage object using the ImageIO.read() method.
• Obtain graphics context of the BufferedImage object.
• Using the Graphics2D object to pain the watermark which can be a String, an image or whatever can be drawn with the Graphics2D’s API. But basically, the watermark is usually translucent so an alpha channel is needed.
• Write the output image using the ImageIO.write() method.

Using this technique, you can develop more complex programs that provide watermark-related functionalities such as adding watermarks in batch, embedding watermarks conditionally, etc.

In this tutorial, we introduce code examples for two typical scenarios: textual watermark and image watermark.

 

1. Java code example to add textual watermark for an image

The following utility method adds a textual watermark over an image. The code comments are self-explanatory:

/**
 * Embeds a textual watermark over a source image to produce
 * a watermarked one.
 * @param text The text to be embedded as watermark.
 * @param sourceImageFile The source image file.
 * @param destImageFile The output image file.
 */
static void addTextWatermark(String text, File sourceImageFile, File destImageFile) {
	try {
		BufferedImage sourceImage = ImageIO.read(sourceImageFile);
		Graphics2D g2d = (Graphics2D) sourceImage.getGraphics();

		// initializes necessary graphic properties
		AlphaComposite alphaChannel = AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 0.1f);
		g2d.setComposite(alphaChannel);
		g2d.setColor(Color.BLUE);
		g2d.setFont(new Font("Arial", Font.BOLD, 64));
		FontMetrics fontMetrics = g2d.getFontMetrics();
		Rectangle2D rect = fontMetrics.getStringBounds(text, g2d);

		// calculates the coordinate where the String is painted
		int centerX = (sourceImage.getWidth() - (int) rect.getWidth()) / 2;
		int centerY = sourceImage.getHeight() / 2;

		// paints the textual watermark
		g2d.drawString(text, centerX, centerY);

		ImageIO.write(sourceImage, "png", destImageFile);
		g2d.dispose();

		System.out.println("The tex watermark is added to the image.");

	} catch (IOException ex) {
		System.err.println(ex);
	}
}

Example usage:

File sourceImageFile = new File("e:/Test/Watermark/SwingEmailSender.png");
File destImageFile = new File("e:/Test/Watermark/text_watermarked.png");

addTextWatermark("CodeJava", sourceImageFile, destImageFile);

The sample source image:

The output image:

 

 

2. Java code example to add image watermark for an image

And the following utility method adds an image watermark over an image:

/**
 * Embeds an image watermark over a source image to produce
 * a watermarked one.
 * @param watermarkImageFile The image file used as the watermark.
 * @param sourceImageFile The source image file.
 * @param destImageFile The output image file.
 */
static void addImageWatermark(File watermarkImageFile, File sourceImageFile, File destImageFile) {
	try {
		BufferedImage sourceImage = ImageIO.read(sourceImageFile);
		BufferedImage watermarkImage = ImageIO.read(watermarkImageFile);

		// initializes necessary graphic properties
		Graphics2D g2d = (Graphics2D) sourceImage.getGraphics();
		AlphaComposite alphaChannel = AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 0.3f);
		g2d.setComposite(alphaChannel);

		// calculates the coordinate where the image is painted
		int topLeftX = (sourceImage.getWidth() - watermarkImage.getWidth()) / 2;
		int topLeftY = (sourceImage.getHeight() - watermarkImage.getHeight()) / 2;

		// paints the image watermark
		g2d.drawImage(watermarkImage, topLeftX, topLeftY, null);

		ImageIO.write(sourceImage, "png", destImageFile);
		g2d.dispose();

		System.out.println("The image watermark is added to the image.");

	} catch (IOException ex) {
		System.err.println(ex);
	}
}

Example usage:

File sourceImageFile = new File("e:/Test/Watermark/SwingEmailSender.png");
File watermarkImageFile = new File("e:/Test/Watermark/CodeJavaLogo.png");
File destImageFile = new File("e:/Test/Watermark/text_watermarked.png");

addImageWatermark(watermarkImageFile, sourceImageFile, destImageFile);

The sample source image:

The watermark image:

The output image:

 

Other Java Graphics Tutorials:

• How to resize images using Java
• How to convert image format using Java
• How to capture screenshot programmatically in Java
• How to draw text vertically with Java Graphics2D
• How to draw image with automatic scaling
• Creating Zoomable User Interfaces Programs with Piccolo2D Framework
• Drawing lines examples with Java Graphics2D
• Drawing Rectangles Examples with Java Graphics2D
• Using JFreechart to draw line chart with CategoryDataset
• Using JFreechart to draw XY line chart with XYDataset