This Python class is a simple proof of concept for generating "fake" JPEGs quickly. You "train" it with a collection of existing JPEGs and, once trained, you can use it to generate an arbitrary number of things that seem like JPEGs.
This is part of my attempt to safeguard my web server from aggressive web crawlers. It's designed to run very quickly, so that it can feed fake JPEGs to those crawlers on the fly.
The fake JPEGs do not contain valid compressed data, since generating a valid compressed stream from generated pixel data would be slow. Instead, wherever compressed pixel data is required, the generated files contain random bytes. The result is something that, structurally, appears to be a valid JPEG and for which most JPEG decoders will generate an actual image. Most decoders will report warnings about bad Huffman codes, since the data is not correctly structured.
Every web browser I've tried has silently accepted the resulting data and rendered an image.
The general idea is to have a simple Flask application which can provide an infinite supply of images on demand, without placing much load on your web server. On my web server, the class can generate over 500 1280x1024 JPEGs per second.
I'm not going to give too much detail in how to use this code, at this point. If you're not fairly familiar with deploying web applications and managing web server load, you probably don't want to be playing with this!
- Python and Flask. On Debian,
apt-get install python3-flaskshould get you all you need. - A working web server with the ability to run Python WSGI applications. For example, Apache with mod_wsgi.
The file, index.wsgi is an example implementation of a page
which, when correctly set up, will generate pictures on demand. The
script expects to find a file named "jpeg_templates.pkl" containing
a pre-trained FakeJPEG image. I'm supplying an example pickle file,
generated using the "make_templates.py" script from this repo.
To use this script, you'd want something like the following in your Apache config.
WSGIDaemonProcess fakejpeg threads=10 maximum-requests=10000 user=fakejpeg-user group=fakejpeg-group
WSGIScriptAlias /fakejpeg-example /path/to/fakejpeg/index.wsgi process-group=fakejpeg application-group=%{GLOBAL}
In the above, fakejpeg-user and fakejpeg-group are the username and
groupname of a user that the application should run as.
Once Apache has been restarted/reconfigured, you should be able to access any URL under the /fakejpeg-example/ and receive a fake JPEG file back, which your browser should hopefully render. It'll be a garish mess, but I hope it'll give those aggressive crawlers something to chew over.
These were generated using "make_examples.py" and "jpeg_templates.pkl".
