Image Watermark
Image Watermark lets you add customizable text watermarks directly in your browser without uploading images. The tool uses client-side OffscreenCanvas rendering to overlay text efficiently and privately.
Image Watermark enables you to apply text watermarks on images using client-side processing with OffscreenCanvas, ensuring that no data leaves your device for full privacy. The tool supports opacity control from 5% to 100%, white fill with black stroke for legibility, and three positioning modes including center, diagonal, and bottom-right. By working entirely in the browser, Image Watermark prevents any image upload, safeguarding your files. You can also complement watermarking with image adjustments using related tools like Resize Image and Crop Image.
How to Use Image Watermark
- Upload your image file directly into the tool; no upload to any server occurs.
- Enter the watermark text and set font size between 12 and 200 pixels.
- Choose watermark position: center (single text), diagonal (rotated -45°, repeated vertically), or bottom-right aligned.
- Adjust the watermark opacity from 5% to 100% using the slider for subtle or prominent marks.
- Review the preview and download the watermarked image in the original format.
How It Works
This tool uses OffscreenCanvas for client-side image and text rendering, which improves performance and reduces UI thread blocking. It first draws the original image onto the canvas, then overlays the watermark text using ctx.globalAlpha to control transparency.
Text is drawn with a white fill and a 2px black stroke to ensure visibility on both light and dark backgrounds. The watermark can be positioned in three ways: center (single text), diagonal (rotated by -45 degrees and repeated 5 times vertically), and bottom-right (right-aligned). The font is a sans-serif style with customizable size from 12 to 200 pixels, allowing fine control over watermark appearance.
All processing occurs within the browser, so your image data never leaves your device, ensuring privacy and security.
Example
Input Image: 800x600 JPEG photo
Watermark Text: "Sample"
Font Size: 48px
Position: Diagonal
Opacity: 30%
Output: 800x600 image with repeated "Sample" watermark text rotated at -45°, semi-transparent at 30%, visible on all backgrounds due to stroke and fill.When to Use Image Watermark
- Developers needing to protect UI mockups or screenshots before sharing in public repos.
- Designers marking portfolio images with branding to deter unauthorized use.
- SEO specialists adding subtle watermarks to images on websites to maintain ownership while preserving aesthetics.
- Students or educators preparing images for presentations with identification marks.
- Anyone requiring offline image watermarking without exposing files to cloud services.
For further image manipulation before watermarking, consider using Resize Image to adjust dimensions or Crop Image to select specific areas. You can also rotate images with Rotate Image or flip them using Flip Image to prepare images optimally.
Frequently Asked Questions
Does Image Watermark upload my images to a server?
No, all image processing happens entirely in your browser using OffscreenCanvas. This means your images never leave your device, ensuring complete privacy and security.
What file formats does Image Watermark support?
The tool works with common web image formats such as JPEG, PNG, and GIF. Since rendering occurs in the browser canvas, it supports any image format your browser can decode.
How does the watermark opacity setting work technically?
Opacity is controlled via the canvas context's globalAlpha property, which accepts values between 0.05 (5%) and 1 (100%). Adjusting this value changes the transparency of the watermark text overlay.
Can I customize the font and position of the watermark?
Yes, you can set the font size between 12 and 200 pixels and choose from three preset positions: center (single text), diagonal (rotated -45°, repeated vertically), or bottom-right (right-aligned). The font is a sans-serif style for readability.
Will the watermark be visible on both light and dark images?
The watermark uses a white fill with a 2px black stroke to ensure high contrast and visibility across light and dark backgrounds, maintaining legibility regardless of image content.
Can I combine Image Watermark with other image editing tools?
Absolutely. You can resize, crop, rotate, or flip your images using related tools like Resize Image, Crop Image, Rotate Image, and Flip Image before applying your watermark.