Learn Dutch: De foto middenboven is immers te klein. - The photo top center is too small, after all.

When combining spatial adverbs in Dutch, the horizontal position (links, rechts, midden) always comes before the vertical position (boven, onder). While English says "top center" (vertical then horizontal), Dutch builds it the other way around: middenboven.

Why is middenboven placed directly after De foto instead of before it?

middenboven is an adverb of place, not an adjective. Because it is an adverb, it cannot be placed in front of the noun (you cannot say De middenboven foto). Instead, it sits right after the noun it modifies, acting like a shortened relative clause: De foto (die) middenboven (is).

How would I form other exact corners based on the pattern in middenboven?

You use the exact same horizontal-first pattern. "Top left" becomes linksboven (literally "left-top") and "bottom right" becomes rechtsonder ("right-bottom").

What exact nuance does the word immers add to this sentence?

immers is a modal particle that translates best to "after all" or "as you know". It shows the speaker is using the photo's small size as a justification for something, and they assume the listener already knows this fact or will easily agree with it.