Thank you for your comments! For sure, the CNN is expressive for learning the characteristics of images. However, in this development, I tried to not use deep-learning because I believe that it is important to provide fast, consistent results without the need for training data. If you are particularly interested in this app, I would be glad if you could create a pull request to extend the algorithm.
The parent comment said nothing about using deep learning. Convolution is not the same as using a CNN. I interpreted their comment as meaning they used a 2D convolution (presumably a 2D cross correlation, actually) to find regions of overlap
Thank you for comments! Certainly, this application may not be able to handle any kinds of images. However, I tried to stitch images without using deep-learning. Therefore, the strength of this app is that when this app receives the same images, it always produces consistent results. In the future, I will try to develop a more effective image merging method in more generalized scenario.