You have control over the theme of Password Reset Server (PRS), depending on how much effort you want to put into it. To change the logo, perform the following steps:
Go to the PRS Application folder on the web server and find the Themes folder, and make a copy of "PasswordResetServer - Default", and rename the copy to something you desire. This new name will be used to identity the theme when you go to PRS configuration.
Going into the new theme folder you just renamed, you should find an "images" folder, in it you should find "prs_logo.png" This is the logo that is display on top left of the page. You can change this image to anything you want, but the original dimension, which is 300x50 is recommended. Same goes for the background, which is based on the "bg.jpg" image.
This should do it if you wanted to replace the logo and background. If you need further customization, you can go to the Style folder and tune the CSS file to have PRS look however you want.
The last step is to set PRS to use your new theme. You can do so in the app by going to Administration -> Configuration, and you should find the theme with your personalized logo from the Default Theme drop down list. Select it and choose Save.
NOTE: Once you have copied an existing theme, you can customize any element of PRS whether it be CSS or images by changing the CSS or images in your new theme.