Unfortunately, I cannot find a setting to increase quality/resolution of pictures which I uploaded to the Wiki. If I click the image at the side of the wiki the resolution and size is fine. It's just a problem when the image is embedded in the text of the wiki. Additionally, there is no option enlarge images uploaded to the Wiki (as e.g. in Confluence by clicking on the image).
I am not sure we entirely understand your issue.
For better readability of text, the Wiki uses the common practice of enforcing a maximum width. Images size automatically at the same maximum size as the text:
Would you want the images to become bigger than the text? Or something else?
Yes, I think if the image would become broader than the text this would resolve the problem. Since the image is pretty wide but not long.
Another solution would be if I could link an image to the attachment. What I mean is that I get the same functionality by clicking on the image as if I click on the attachment on the sidebar (of the Wiki). Thus if I click on the image a new browser tab opens and I see the image in its original size.