You may stitch certain photos to form a panorama using software like e.g. Microsoft ICE (Image Composite Editor). There are other tools available, search the Internet for "stitch panorama"... The result of stitching quite often is a panorama, in which the horizon is not perfectly straight. The effort you then have to spend to straighten the horizon is always quite some hell.
This was the reason, why I wrote a JavaFX based tool to simplify this process.
|Before - after straightening Screenshot|
Please feel free to use the tool, if you want to use it. Installation is available here: http://captaincasademo.com/horizon/setup_launcherfx.exe
Some documentation is available here: http://captaincasademo.com/horizon/20150619_PanoramaHorizonStraightener.pdf
The tool comes as .exe-setup program for Windows. The default installation location is your user's local directory. Please do NOT install it in Windows/Program Files! The installation contains "everything" that is required to run the tool (including the Java runtime).
Forgive me for not providing a MaxOS installer yet - it's just my lazyness...