When you insert an image that is larger than the width of the widget you are in inserting the image into (in pixels in the x direction), the image will either get "resized" to the pixel width of the widget or the image will get "cut off" on the right side. To avoid this when inserting an image in a wiki article, forum post, or blog article, you need to do a few things to make sure it can be viewed at its original size.
When you insert an image in a post or article,
change the default 550 pixels for the "Max width" setting to be the width (in pixels) of the original image.
If you are using Chrome or Firefox, you can right-click on the image in the resulting post or article and open that in a separate view/tab.
For Internet Explorer, you need to zoom in using that browser's zoom function (found under Tools, or Alt-X).
You may need to adjust the pixel width value, but making that larger than the default should provide some form of ability to zoom in to images that have a lot of detail.