Install the module using composer and add Argus, together with WebDriver, to the modules in your suite.yml file, and sprinkle $I->eyeball("filename/description") through your test.

Run your tests and they should fail due to new screen-shots. Look through all the *.result.png files and make sure they look as they should, and rename them to *.original.png.

Now Argus will compare the screen-shots of new test runs with the originals and fail if detecting any differences. It will also leave the new *.result.png file and a *.diff.png highlighting the differences for inspection. Replace the *.original.png file with the corresponding *.result.png to accept the changes, or fix the error.