[SalesForce] How to put image in Community Login page

I hope I understand your question correctly. So you want to redirect a community user to a VF page?

One thing what I did for one of my recent projects is to create a Tab (in this case "Player Dash Board") for my Visualforce page that I want the user to land on, instead of the Home page. Then in the Community setup I removed all the other tabs. You could have the other tabs in there, but the Community loads the first one that is there in the below list.

What do you mean when you say it doesn't work? What results are you getting exactly?

You should be fine simply with:

public PageReference Login() {
  return Site.login(username, password, null);
}

This will forward successful login attempts to the page you define in the community setup page:

Setup > Communities > [Community Name] > Manage > Administration > Pages > Community Home

Unsuccessful login attempts will cause Site.login() to return null. Therefore you can check for this and, if null, display an error message to the user.

For more information, see the "Customize Your Community’s Login Experience" section of the Getting Started With Communities guide.