Creating a basic structure in tkinter
Any tips on how to improve it so I am not repeating code?


There isn't really a lot of repeated code, here. I think you're fine on that front.

Avoid globals

Starting with image1 onward, you have lots of globals. Try to move them into a class, for a few reasons: re-entrance (you could spawn multiple identical windows), general code organization, namespace cleanliness, etc.

Credential management

if ent1.get() == 'admin' and ent2.get() == 'password':


I know that you are


  making a basic program just for a local machine


but this is never a good habit to get into. Hard-coding passwords is not secure, and it isn't much more difficult to do the "right" thing. Import a library to be able to securely handle authentication and encrypted credential storage.