Show IH: I built a privacy-first bulk watermarker that runs 100% in the browser

Hi IndieHackers! 👋

I recently started selling items on second-hand platforms (like Vinted and Depop) and quickly realized a painful bottleneck: watermarking product photos.

Existing tools were either:

1. Slow: Uploading 50+ images to a server takes forever.

2. Privacy-invasive: I didn't feel comfortable sending personal photos to unknown servers.

3. Full of ads: The user experience was often terrible.

So, I decided to scratch my own itch and build Smart Watermark Tool.

🚀 The Tech Stack I wanted the tool to be fast and completely secure, so I went with a Local-First approach.

• Framework: Next.js (App Router)

• Styling: Tailwind CSS (Shadcn/ui vibe)

• Processing: HTML5 Canvas API (for image manipulation) + JSZip (for bundling downloads)

• Deployment: Vercel

✨ Key Features Since it runs client-side, your images never leave your device.

• Smart Contrast: I wrote a small algorithm that calculates the luminance of the image area where the logo sits, automatically switching the watermark to black or white for best visibility.

• SEO Renaming: It prompts you to rename files before downloading (e.g., vintage-jeans-01.jpg), which is crucial for ranking on marketplaces.

• HEIC Support: It automatically converts iPhone HEIC photos to JPG in the browser.

💸 Monetization Currently $0/mo. It's a free tool. I built it to solve a problem and improve my portfolio.

🙏 Feedback Request I just launched it on Product Hunt and I'm looking for feedback on the UX. specifically:

• Is the "drag & drop" flow intuitive?

• Does the "Smart Contrast" work well on your images?

You can try it here: https://smart-watermark.vercel.app/

Thanks for checking it out! (tino8383)