I really liked the styling on the website.
The concept itself is interesting, something about opening journal entries has a calming effect. Making it login only is a bit off-putting.
Hey, you might want to experiment with local sync approach by allowing devices to sync when are on the same network. I have never done this so there might be hurdles, but this can bypass the issues with cloud sync while maintaining the ability to sync across devices
I recommend you to show an example and a result for people to understand exactly what the tool does. As far as i know "merging images" is not a common term with a specific meaning.