How to undo image resizing in lightbox?

Question

Joomla

Hello,
On my test site, I placed a scanned document in the lightbox on the right. I have Joomla 3.6.2
Here is the site URL:
idevsky.com
The lightbox module is a Custom HTML module with the following code:

<p><a class="spotlight" href="images/document2.jpg" data-lightbox="on" data-demo="group:mygroup1" data-spotlight="on"> <img src="images/document2.jpg" alt="demo" width="98" border="0" /></a></p>

My screen resolution is 1366x768. Full image size W 583px H 800 px. When I click on the icon and the document opens in full size, for some reason it is 50% smaller somewhere. You can see this in my screenshot which I am attaching here. As I was told by those who have Full HD (1920x1080), then their document opens in full size. Apparently, there is responsiveness here, depending on the screen size.
One way or another, I would like the picture to open completely and equally at all resolutions (I'm not talking about mobile here, that's different).