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Train a CNN model to identify captcha code with TensorFlow and Keras

In the last post (Automatically fill in captcha code in course selection system), we exploited the "Play Audio" button function to obtain the captcha code in the course selection system from my college. Today, we will be going through another approch to identify the captcha code by training a CNN model with TensorFlow and Keras.

A captcha code from the course selection system.


Install Needed Packages

Below are the environment and package versions that I perform the training in this post.

MacOS 10.14.6
Python: 3.7.3
numpy: 1.18.0
scikit-learn: 0.22
TensorFlow: 2.0.0
Pillow: 6.2.1

If lacking any of these packages, just simply install them with the following commands.

NumPy: pip install numpy
scikit-learn: pip install scikit-learn
TensorFlow: pip install tensorflow
Pillow: pip install Pillow

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Automatically fill in captcha code in course selection system

Captcha code is broadly used in different websites to ensure the contents are only accessible by humans rather than bots. The course selection system in my college has also been adopting captcha code in the login page to reduce momentary load of its server. (by slowing down everyone's time to fill in the code and hit log in)

Besides that, the system was kindly designed a "Play Audio" button as well for visually impaired people to "hear" the captcha code. However, it becomes a defect that we can take advantage of the "Play Audio" button function to fill in the captcha code programmatically for us.

Since I have done my last course selection in my college life, I will demonstrate how to fill in the captcha code by exploiting the "Play Audio" button function in below.

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[Matplotlib] Multiple axes with different scales

It's quite often for me to plot out the statistical data while training machine learning models. E.g., teaching models to play games.

As the records increase, the chart becomes crowded as well as difficult to see how the line grows. Therefore, a strategy come up that only plotting out the average of each 250 records in a chart.

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[Java] Convert SQL ResultSet to JSON Array

JSON is a handy format while dealing with data in front end. However, we can't directly obtain JSON array if we are using Java querying data from database via JDBC. The default return type of querying data via JDBC is ResultSet.

Fortunately, below is an approach I found to convert SQL ResultSet to JSON array.

Remember to import.

import org.json.JSONArray;
import org.json.JSONObject;
import java.sql.ResultSet;

The convert method.

public static JSONArray convert(ResultSet resultSet) throws Exception {

	JSONArray jsonArray = new JSONArray();

	while ( {

		int columns = resultSet.getMetaData().getColumnCount();
		JSONObject obj = new JSONObject();

		for (int i = 0; i < columns; i++)
			obj.put(resultSet.getMetaData().getColumnLabel(i + 1).toLowerCase(), resultSet.getObject(i + 1));

	return jsonArray;


where I found the code