Although the customer may not delete an uploaded logo image if they change their mind, a workaround exists.
You can give your customers the option of choosing a logo or not by creating a Value Question, and then using rules to enable or disable your logo question based on their answer to that value question.
Create a Value Question called Add a logo? with 2 answers : Yes and No
Create your Logo Question, let's say it's named Logo
Create a rule like this one :
When Add a logo? is Yes then Logo should be unavailable.
To hide the Logo questions when it's not available, make sure to enable the 'Hide when empty' setting.