Ok, I just understood something and so I will clarify: the difference comes from the way in which the image is added, if we add it through the feature thread manager then it is displayed slightly zoomed, if we leave the image original, posted in the thread, then it displays correctly.
Can you tell me why add the same image in the feature thread manager? Well it was to test the system, and it helped to discover that, perhaps, the way the images added in the manager are displayed incorrectly afterwards.
Otherwise I can understand your thinking on the fact that you thought it wasn't a bug but I don't think this discussion is better placed in Styling and customization question rather than in Troubleshooting and problems. I notice a possible malfunction, I am not asking how to customize anything.