I couldn't find a tool that could split images exactly how I wanted, so I made one myself.
It's handy for combining printed A4 images into a large poster or creating stylish grids and continuous images that you sometimes see on social media like Instagram and Threads. It works on iPhone/iPad/Android, so please check it out!
What can it do?
Split vertically and horizontally into any number of pieces
For my purposes, I needed to be able to split into quite a few vertical and horizontal pieces, but I couldn't find a service that could do that (or if it could, it didn't meet the next requirement). So I made it able to split extremely finely.
As long as the split images are at least 1px vertically and horizontally, it should work.
Split into any rectangle
You can specify the aspect ratio of the split images. Common shapes like 1:1, A4 portrait, A4 landscape can be easily set. If you don't care about the shape after splitting, choose Free.
How to use
Decide the shape after splitting
You can set it to the shape you like by entering it in Horizontal : Vertical.
Decide the number of vertical and horizontal divisions
You can also enter the number of vertical divisions from 目 on the right.
Split
Click the check mark to save the image to your device.
Install
You can install it from here, so please do!