Replace argument by parameter in image.py

[michaelgrund]

Replaced all appearances of argument by parameter.

[seisman]

Just a quick comment: I don't quite like this example, because it's so similar to the "logo" example (https://www.pygmt.org/dev/gallery/plot/logo.html). Perhaps we can change to a better image?

[michaelgrund]

Just a quick comment: I don't quite like this example, because it's so similar to the "logo" example (https://www.pygmt.org/dev/gallery/plot/logo.html). Perhaps we can change to a better image?

Agree with you @seisman , any suggestions which image we could use instead? Originally I selected this image since it is availabe from the GMT website, so we would know if its origin changes. Alternatively, we could store an example image in the repo.

[seisman]

Close this one as the changes has been merged into #943. We may still want to improve the example using a better figure.