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It we take Wittgensteins picture theory of language for granted,
The picture theory of meaning states that statements are meaningful if, and only if, they can be defined or pictured in the real world
Then how would he possibly explain that blind people can learn a language?
Pointing is not meant physically, but logically. In the same way seeing is meant conceptually, as a metaphor.
"In this sort of predicament, always ask yourself: How did we learn the meaning of this word ("good", for instance)? From what sort of examples? In what language-games? Then it will be easier for you to see that the word must have a family of meanings."
-Wittgenstein, in Philosophical Investigations
He argued that we learn meanings through language games, developed through engaging in shared forms of life, for instance by contextual relationship of an utterance to an experience. Although a blind person can't share experiences of physical space, they do have spatial awareness, and develop spatial mental maps, see eg Mental Maps and the Use of Sensory Information by Blind and Partially Sighted People. We also know people who become blind, in time reorganise their visual cortex to respond to non-visual information, see eg Visual Cortex Activity in Early and Late Blind People. So there is logical experience of spatial information, seperate to visual stimuli. Echo-location in bats and dolphins, and electrosenses in sharks and many fish, shows how sight can become a secondary sense for delivering spatial information.
A blind person could engage in the Paralympic sport of blind football, developing their understanding of the word 'game' in the same way as a sighted person engaging in and learning a specifuc game. Wittgenstein drew attention to the 'fuzziness' and flexibility of the term 'game', and used that in developing his terminology 'language game'. See eg Wittgenstein on the definition of a ‘game'
See further discussion here, which includes some relevant cases: According to the major theories of concepts, where do meanings come from?
You seem to be missing the point that the picture theory of meaning is so called because a picture is an example to illustrate his theory. A picture stands in a certain relationship to its subject (what it is a picture of). Another common example is the relationship between the written score of a piece of music and the music as played and a recording of a performance.
In a word, these are all cases of same structure. The elements of the picture (the patches of colour), when they are arranged in a certain way, represent the scene being pictured. Similarly, the elements of the score, the performance, the recording, when they are arranged in a certain way represent (or present) the music.
Once we understand that relationship we can see the picture as a picture of something else, which is quite unlike it. When we understand the relationships in the score, we can play the music and construct a technology to record it.
The general concept is complicated, but the application to language is very tempting. It starts from the truth-functional calculus, the correspondence theory of truth and the idea that some propositions are atomic, because when they are analysed into words, they lose their sense (capacity to be true or false).
I won't go further with this, because I think I've explained that the Tractatus theory in no way presupposes that language learners need to be able to see. SEP - Logical atomism
I don't know how difficult it is for a person blind from birth to learn a language. But it is probably much more difficult for someone who is deaf from birth to learn language, and for someone who is deaf and dumb more difficult still. Helen Keller (who was deaf-blind) is a famous case in point. Wikipedia - Helen Keller
Your question arises from an empirical reading of Wittgenstein. He was never an empiricist, as a young man he was heavily influenced by Kant and Schopenhauer (although later on he called Schopenhauer a "crude mind"), and he knew that there are a priori truths that are prior to and superior to the empirical truths.
Blind people CAN picture structure as such. They know what it means for a thing to be next to another thing, to be before / after, to be bigger / smaller etc etc. Their rational cognitive faculties are intact, and they have access to the a priori truths. That is all that matters. Yes, they may not know what a red Lamborghini looks like, but that does not matter.
What matters is structure, empirical data is secondary. For Wittgenstein, meaning is related to logic, which is a priori. Sight is an empirical faculty.
