"Canon" is not about individual details, but broad strokes. There are countless details in any long-running series that contradict each other, that are ignored by later installments, or that are simply mistakes. It's important not to forget that a canon is a work of fiction -- it's one author or a group of filmmakers and actors telling stories about an imaginary reality. The pretense is that there's a "real" world underlying it all, but the way the storytellers depict the details of that reality is subject to error, differences of interpretation, or changes of mind.
Is it "canonical" that there's a giant rubber ducky somewhere inside the Enterprise
-D, or that Yoyodyne Propulsion had a shop on the Promenade? You might as well ask if it's canonical that NCC-1701's nacelle struts blinked out of existence in that matte shot in one episode, or if it's canonical that Sylvia and Korob's true forms had wires puppeteering them, or if it's canonical that Saavik had extensive plastic surgery right after Spock's funeral, or whatever. Of course none of those are part of the imaginary underlying reality that we think of when we refer to the canon. They're part of the way that reality is interpreted by the creators of the fiction, and they can't be taken too literally. Think of it like how different comic-book artists draw the same character, or the way different actors play the same character. Different writers, directors, set designers, etc. also bring their own differences of interpretation to the work. When different people work on the same thing, there are bound to be inconsistencies in the details. But the audience is expected to suspend disbelief about the minor inconsistencies or errors and buy into the pretense that there's a consistent underlying reality. That's what canon is supposed to be -- a thing of the broad strokes, not the niggly details.
So no, barely legible graphics are not "canon" any more than any other single detail is "canon." Canon is the overall aggregate that you see when you step back and look at the whole. An individual detail may be relevant to the whole or it may just be a joke, mistake, or inconsequential bit of scenery.