You can put it in the wwwroot folder. Such as: wwwroot\images\background.jpg
And then set it as the html's background image in the wwwroot\css\app.css:
html, body { font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; background-color:transparent}html { position: relative; min-height: 100%; background-image: url(../images/background.jpg); background-position: center; background-repeat: no-repeat; background-size: cover;}And the result:
