All depends on if that it is on local pc or provided with ftp access from web provider, but essencialy approach is similar.
For local instalation, locate your Tomcat instalation directory, go to webapps folder, then open your project to which you wish to add images for example MyProject and then you on top level for given project.
For hosted you need to access the server throught ftp, details of which your web provider should give it to you. In this case there is only one project so you get directly to the top level of project.
Once on top level (for both cases) I recommend for organisation reasons, you create new folder, you may name it img and copy&paste or upload your images.
If Tomcat running on Unix based system do not forget set up access permissions for images and also for folder if created