Images should be smallest size possible, in both their dimensions and file size. If on a Mac using a program like imageOptim can help strip out any other extra data and make the files smaller. Also the format will also help adjust the file size optimizing the image more.

For Desktop, cover images need to be no larger than 1600px
For mobile, images need to be no smaller than 480px
All images should be under 1Mb in file size.

Did this answer your question?