I ran a file in GTMetrix and it tells me that an image is not scaled. In the HTML the size is exactly that of the image. And in the css I can’t see anything affecting directly the size of the image.
Why is the error coming up, and how can I solve it, please?
Its natural dimensions are 599px x 398px but in your normal width page you are displaying it at a max-size of 406px x 306px. Therefore the check you ran is informing you that you would be better off with an image that is 406px x 306px to start with.
However, what the checker failed to notice is that at smaller screen sizes you actually show the image larger when 3 columns go to one so the advice is incorrect.
These automated checkers never know the whole story and so you should use their results as a guide and not as the ultimate truth:)
Yes, that’s fine but the only downside is that on smaller screen you get the bigger image which won’t look so good. However its always a trade off and a smaller file size is often a better option against slightly lesser quality.