After weeks of research I have nearly completed my thesis, yet I am unable to clear up my confusion contained in all previous threads here (and in many books):

During system testing, we check the system function against system analysis (functional system design) - but that would fit to a definition of verification according to many books. But I follow ISO12207, which considers all testing as validation (making sure work product meets requirement for intended use). How can I justify that unit testing or system testing is validation, even though when I check it against specification? Which fullfils the definiton of verification? When testing that e.g. "Save button" works, is it validation?

This picture shows my understanding of V&V, so different from many other sources, including ISTQB etc.

Essential problem I have is that a book using the same picture also states on another place that:

test activities in the area of validation are usability, alpha and beta testing. For verification, testable system requirements are defined whose correct implementation can be tested through system tests.

Isn't that the opposite of what the picture says? Most books present the following picture, where validation is just making sure that customer needs are satisfied. Mind you that according to ISO, validation activity is testing.