PHP verification code does not display solution

Solution:

1. Check whether PHP has the GD extension installed and turned on; (Recommended to learn : PHP video tutorial)

2. The reason for the utf-8 BOM header. Use Editplus or ultraedit to delete it. (https://blog.csdn.net/oscar999/article/details/6280006)

3. Caching problem in the output buffer. Before output, use the ob_clean function to solve it.

4. Before output, echo, print_r, var_dump, etc. cannot appear. Comment or delete to solve the problem.

The code after solving the problem:

The result is displayed as follows:

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