Two points:

Since you are using a 300dpi image and displaying at 72dpi. the browser has to resize it every time someone views it, which is generally quick & dirty, and less effective/graceful than Photoshop's rendering.

You have a huge image file (1196 kb) which takes a long time to download on slower connections. This is bad.

What you should do is make a copy of the image in Photoshop or whatever that is the exact pixel size you want it to display at. This will load faster and look better.