How to add watermarks and copyright information to images in Go?

To add watermarks and copyright information to images in Go, you can use the github.com/disintegration/imaging library. Here's an example of how to add a watermark and copyright text to an image:

package main

import (
	"image"
	"image/color"
	"image/draw"
	"image/font"
	"image/jpeg"
	"log"
	"os"

	"github.com/disintegration/imaging"
	"golang.org/x/image/font/basicfont"
)

func main() {
	// Open the original image file
	file, err := os.Open("input.jpg")
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	// Decode the image file
	img, _, err := image.Decode(file)
	if err != nil {
		log.Fatal(err)
	}

	// Create a new image with the same size as the original image
	watermarkedImg := imaging.New(img.Bounds().Dx(), img.Bounds().Dy(), color.Transparent)

	// Copy the original image to the new image
	draw.Draw(watermarkedImg, watermarkedImg.Bounds(), img, image.Point{}, draw.Src)

	// Add the watermark image
	watermark, err := imaging.Open("watermark.png")
	if err != nil {
		log.Fatal(err)
	}

	// Resize the watermark image to a desired size
	watermark = imaging.Resize(watermark, 200, 0, imaging.Lanczos)

	// Position the watermark image at the bottom right corner of the main image
	pos := image.Pt(watermarkedImg.Bounds().Dx()-watermark.Bounds().Dx()-10, watermarkedImg.Bounds().Dy()-watermark.Bounds().Dy()-10)
	watermarkedImg = imaging.Overlay(watermarkedImg, watermark, pos, 1)

	// Add the copyright text
	copyrightFontFace := basicfont.Face7x13
	copyrightFontSize := 16
	copyright := "Copyright © 2022 Your Name"
	PutLabel(watermarkedImg, 10, 10+int(font.MeasureString(basicfont.Face7x13, "A").Ceil()), copyright, copyrightFontFace, copyrightFontSize, color.White)

	// Save the watermarked image
	output, err := os.Create("output.jpg")
	if err != nil {
		log.Fatal(err)
	}
	defer output.Close()

	// Encode the watermarked image as JPEG
	err = jpeg.Encode(output, watermarkedImg, &jpeg.Options{Quality: 100})
	if err != nil {
		log.Fatal(err)
	}
}

func PutLabel(dst draw.Image, x, y int, label string, face font.Face, size int, color color.Color) {
	d := &font.Drawer{
		Dst:  dst,
		Src:  image.NewUniform(color),
		Face: face,
		Dot:  fixedPoint26_6(x, y),
	}
	d.DrawString(label)
}

func fixedPoint26_6(x, y int) fixed.Point26_6 {
	return fixed.Point26_6{
		X: fixed.Int26_6(x * 64),
		Y: fixed.Int26_6(y * 64),
	}
}

In this example, we first open the original image file using os.Open and decode it into an image.Image using image.Decode. We then create a new blank image with the same size as the original image using imaging.New and copy the original image onto the new image using draw.Draw.

Next, we open the watermark image file using imaging.Open and resize it to a desired size using imaging.Resize. We then position the watermark image at the bottom right corner of the main image using imaging.Overlay.

To add the copyright text, we use a custom PutLabel function that draws the text on the watermarked image. This function uses the basicfont.Face7x13 font face from golang.org/x/image/font/basicfont. You can customize the font face and size according to your preference.

Finally, we save the watermarked image as a JPEG file using jpeg.Encode. You can change the output format or adjust the quality according to your needs.

Make sure to replace the "input.jpg", "watermark.png", and "output.jpg" file paths with your own file paths.