"Much" refers to something not countable, like "much more milk", and is used without plural, "liter" is countable such that you could say "many more liters of milk" (note the plural of liter). So while I'd say the latter is more correct according to grammatical rules, if both are common, both can be considered correct, as rules are often rewritten to adapt to the way the English language is used.
That was my reasoning, which is correct in my native language (Spanish: "muchas más imágenes). That's why seeing more results for "much more images" suprised me.
No, I mean I got 43 results on a Google search for the first quoted phrase, and 3.1M for the second quoted phrase. That's two separate G searches. I was not looking for documents with both phrases.