This is a simple implementation to hide a message inside an image. You can upload an image, insert your message and then download the image. When you upload an image which contains a secret message you can see this message in the textbox (otherwise it will look like mojibake).
This tool is available on https://nikolockenvitz.de/steganography but you can also download the repository and run it locally/offline.
If you really want to use steganography to communicate secretly, I highly recommend to encrypt the message before.
This application is still in development, some more advanced features are planned (e.g. hidden images, QR-Codes, encryption, ...). If you like you can fork this repository and add some features or optimize existing code. In case you have questions feel free to ask me.