How to work with images when creating from a PSD layout?

Question

css

I study layout and for practice I type PSD layouts from the htmlacademy mailing list, the images in which are often larger than their visible part. Hence two questions.
1. Should I crop images to their visible size before exporting to .png or crop them with CSS?
2. In the final version of the layout, the visible part of the image should be the same regardless of the screen size?

Answer 1

Of course, crop to the maximum size that should be in the email/website. Why do users need extra kilobytes?

Answer 2

It depends on the specific layout what the designer meant there - if there are conditional clouds at 2560px, then obviously they should not be squeezed to fit the screen.
And if it’s a completely solid image, then ask him how it will look at different resolutions.