Regarding the second point—that seeing involves an act of interpretation—Wittgenstein points out that an interpretation requires thought. I can interpret pictures, but I by no means always interpret them. We have no reason for claiming even that there is a different mental act in the person seeing the duck and the person seeing the rabbit. Imagine someone who has grown up in a town filled with ducks, but has never seen a rabbit before. There is no mental act of "seeing it as a duck," because he does not even have the capacity to see it as a rabbit. This is not a shortcoming in his visual or mental apparatus, but simply a fact about his experience.
H. P. Grice, among others, has criticized this line of criticism against sense data theory. Grice argues that this criticism stems from a failure to distinguish semantics from pragmatics. To argue that we do not talk about "seeing a fork as a fork" is simply a matter of linguistic convention, and should have no bearing on the matter at hand. Regardless of what conventions we use to talk about seeing, the fact remains that my visual impressions are not the same as the objects we meet in experience, and it is worthwhile to distinguish between the two.
The objection raised by Grice is a complicated issue, and continues to divide philosophers today. A Wittgensteinian response would take the form of pointing out that we cannot so readily talk about experience divorced from linguistic conventions. A Gricean would set up his sense data theory by using words like "see" and "interpret," and expect us to understand him because he is using these words in ordinary ways.