test_inmemory.go

package main

import (
	"bufio"
	"bytes"
	"fmt"
	"gopkg.in/auyer/steganography.v2"
	"image"
	"os"
)

func main() {
	inFile, err := os.Open("./assets/pre_test.png") // opening file
	if err != nil {
		fmt.Println("unable to open file")
	}
	defer inFile.Close()
	reader := bufio.NewReader(inFile) // buffer reader
	img, _, err := image.Decode(reader)
	if err != nil {
		fmt.Println("ERROR: original image is corrupt " + err.Error())
		return
	}

	w := &bytes.Buffer{}
	err = steganography.Encode(w, img, []byte("this is a watermark"))
	if err != nil {
		fmt.Println(err.Error())
	}

	reader = bufio.NewReader(w)
	img, _, err = image.Decode(reader)
	if err != nil {
		fmt.Println(err.Error())
	}
	sizeOfMessage := steganography.GetMessageSizeFromImage(img)
	msg := steganography.Decode(sizeOfMessage, img)
	fmt.Println("**** " + string(msg))

}

Ran this with both images in your assets folder and it worked fine.

go run t.go 
**** this is a watermark

In the case of the .jpg image, it will work if:

• 1
  Using the "image/jpeg" module to decode img, err := jpeg.Decode(reader)
• 2
  Usage of a init import paired with the default decoding:

  _ "image/jpeg"
  ...
  img, _, err := image.Decode(reader)

@auyer I tested with test.png and it worked, however, I have uploaded pre_test.png (a png without the watermark already) and it doesn't. Does using pre_test.png correctly work on your system?

perhaps something is corrupted in the pre_test.png image?

I will try out the jpg approach now. 👍

jpg test with decode.go, with above approach has this output currently.

$ go run decode.go ./assets/test.jpg 
panic: runtime error: slice bounds out of range

goroutine 1 [running]:
gopkg.in/auyer/steganography%2ev2.decodeRGBA(0xffffffff00000004, 0xc0000b6080, 0xc0000b6080, 0x4, 0x8)
        /Users/scottd/go/pkg/mod/gopkg.in/auyer/steganography.v2@v2.0.0-20190427051610-2664780d40a3/steganography.go:180 +0x5a8
gopkg.in/auyer/steganography%2ev2.decode(0xffffffff00000004, 0x1113040, 0xc00014e080, 0xc0000aa000, 0x1113040, 0xc00014e080)
        /Users/scottd/go/pkg/mod/gopkg.in/auyer/steganography.v2@v2.0.0-20190427051610-2664780d40a3/steganography.go:203 +0x53
gopkg.in/auyer/steganography%2ev2.Decode(...)
        /Users/scottd/go/pkg/mod/gopkg.in/auyer/steganography.v2@v2.0.0-20190427051610-2664780d40a3/steganography.go:217
main.main()
        /Users/scottd/workspace/mattermost-plugin-watermark/decode.go:44 +0x296
exit status 2

it must be the image (for the png issue)... it is working with a new png.