FisheyeGL

Taking images with some cameras will lead to bend images. This effect is called FishEye. Sometimes it fits but sometimes you want to make your picture flat.

For this there is FisheyeGL which is an open source software. It was developed with the knowledge out of the AREN project of the NASA. If you go to their site you can drag&drop your image into the field and change the parameters of your image with the sliders on the right in order to make the image flat.

Here is an example they provide on their website:

Before:

After:

As the project is open source you are able to contribute to this project via their GitHub project.

all images taken from the source