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As I said not on all images but on few, it changes regularly, when I close the site and then open, it occurs on another image.
The images which have white background doesn’t show because the gap is having a white line so it doesn’t appears but the images which have some background colours or images, it shows some gap like I have shown you in the screenshot.
I’m not exactly sure what you meant by this “gap”.
Perhaps you perceive the 5px border as the gap. If so, you can just remove the border: 5px solid rgb(234,236,241); on your CSS and see if that’s the case.
A wise man once said:
"Have you cleared your cache?"