@JonB
Sorry I was too busy due to my works.

I followed your instruction.
But I have an error when I tried this.

pip install urllib3==1.21.1
/private/var/mobile/Containers/Shared/AppGroup/7FD2AC7F-F7F2-40E3-8885-7136C55974E5/Pythonista3/Documents/site-packages-3/requests/init.py:104: RequestsDependencyWarning: urllib3 (1.14) or chardet (4.0.0)/charset_normalizer (None) doesn't match a supported version!
RequestsDependencyWarning)
stash: <class 'ImportError'>: cannot import name 'InvalidHeader'

@JonB
I removed Pythonista and reinstall it.
Then install stash.

(install with this code : import requests as r; exec(r.get('https://bit.ly/get-stash').content) )

Then I did what I wrote just before.

Now I tried again as below;
But there is error.

~/Documents]$ stashconf py_traceback 1
[~/Documents]$ pip install requests
Querying PyPI ...
Downloading package ...
Opening: https://files.pythonhosted.org/packages/2d/61/08076519c80041bc0ffa1a8af0cbd3bf3e2b62af10435d269a9d0f40564d/requests-2.27.1-py2.py3-none-any.whl

Save as: /private/var/mobile/Containers/Data/Application/47FC53DC-CAB6-4B6B-B50F-7EE750FCBB79/tmp//requests-2.27.1-py2.py3-none-any.whl (63133 bytes)
[====================] 100.00% | 61.7KiB
Installing wheel: requests-2.27.1-py2.py3-none-any.whl...
Warning: unknown dependency requirement: 'sys_platform'
Warning: Adding dependency 'win-inet-pton', ignoring requirements for dependency.
Package installed: requests
Installing dependency: urllib3[('<', '1.27'), ('>=', '1.21.1')] (required by: requests)
Querying PyPI ...
Downloading package ...
Opening: https://files.pythonhosted.org/packages/ec/03/062e6444ce4baf1eac17a6a0ebfe36bb1ad05e1df0e20b110de59c278498/urllib3-1.26.9-py2.py3-none-any.whl

Save as: /private/var/mobile/Containers/Data/Application/47FC53DC-CAB6-4B6B-B50F-7EE750FCBB79/tmp//urllib3-1.26.9-py2.py3-none-any.whl (138990 bytes)
[====================] 100.00% | 135.7KiB
Installing wheel: urllib3-1.26.9-py2.py3-none-any.whl...
Warning: unknown dependency requirement: 'os_name'
Warning: Adding dependency 'brotlicffi (>=0.8.0)', ignoring requirements for dependency.
Warning: unknown dependency requirement: 'os_name'
Warning: Adding dependency 'brotli (>=1.0.9)', ignoring requirements for dependency.
Warning: unknown dependency requirement: 'os_name'
Warning: Adding dependency 'brotlipy (>=0.6.0)', ignoring requirements for dependency.
Package installed: urllib3
Installing dependency: brotlicffi[('>=', '0.8.0')] (required by: urllib3)
Querying PyPI ...
Downloading package ...
Opening: https://files.pythonhosted.org/packages/d3/d8/6acbb65e350213ad6bd96180593fad0a269a3baa845c67fed21adee3959d/brotlicffi-1.0.9.2.tar.gz

Save as: /private/var/mobile/Containers/Data/Application/47FC53DC-CAB6-4B6B-B50F-7EE750FCBB79/tmp//brotlicffi-1.0.9.2.tar.gz (440077 bytes)
[====================] 100.00% | 429.8KiB
Extracting archive file ...
Archive extracted.
Running setup file ...
Package installed: brotlicffi
Installing dependency: cffi[('>=', '1.0.0')] (required by: brotlicffi)
Querying PyPI ...
Downloading package ...
Opening: https://files.pythonhosted.org/packages/00/9e/92de7e1217ccc3d5f352ba21e52398372525765b2e0c4530e6eb2ba9282a/cffi-1.15.0.tar.gz

Save as: /private/var/mobile/Containers/Data/Application/47FC53DC-CAB6-4B6B-B50F-7EE750FCBB79/tmp//cffi-1.15.0.tar.gz (484058 bytes)
[====================] 100.00% | 472.7KiB
Extracting archive file ...
Archive extracted.
Running setup file ...
PermissionError(1, 'Operation not permitted')
Failed to run setup.py
Fall back to directory guessing ...
Package installed: cffi
Installing dependency: enum34;python_version[('<', "'3.4'")] (required by: brotlicffi)
Querying PyPI ...
Error: Failed to fetch package release urls

@JonB
Thank you for your patience.
These are what I got from Pythonista in my iPad.

[~/Documents]$ ls site-packages
site-packages/:
Readme.md stash

[~/Documents]$ ls site-packages-2
site-packages-2/:
Readme.md

[~/Documents]$ ls site-packages-3
site-packages-3/:
pip_index.json Readme.md

[~/Documents]$ stashconf py_traceback 1
[~/Documents]$ pip install pip-install-test
Querying PyPI ...
Downloading package ...
Opening: https://files.pythonhosted.org/packages/15/8e/4fbc92846184e1080af77da38d55928a5486e0bc5e2ec8342c7db378d7f1/pip_install_test-0.5-py3-none-any.whl

Save as: /private/var/mobile/Containers/Data/Application/47FC53DC-CAB6-4B6B-B50F-7EE750FCBB79/tmp//pip_install_test-0.5-py3-none-any.whl (1707 bytes)
[====================] 100.00% | 1.7KiB
Installing wheel: pip_install_test-0.5-py3-none-any.whl...
Package installed: pip-install-test

@JonB Thank you for your explanation.

I tried reinstall Pythonista and install stash.
Then remove requests folder(which comes from search (requests) ) and install requests.
When I tried this file fetch error comes.
(exact message - error : failed to fetch package release urls.)

And others also show info file of packages requests(..) not found and similar errors.

ADDED : I just found requests are in standard library(3.6)/site-packages and standard library(2.7)/site-packages.
These are not removable, even it disappear when I send them a trash.
And site-packages, -2. or -3 in a root, there are no requests.

I tried that instruction but there are errors when I install requests and others.
After installing them module error comes even for pip.

is there any step by step instruction for solving this?

There are crashes.

Anyway I just solved this with pythonista.
I used pil instead cv2
Thanks again.

@ccc thanks for your suggestion.
I used pyto but that app is not stable.
And I would like to use pythonista.

image = cv2.imread(image_path)
jpeg_image = cv2.imencode(".jpg", image)[1]
data = jpeg_image.tobytes()

As you know cv2 is not working in pythonista.
But I need to make same as above for ocr api.
Is there any way to do that?