Consider how long children's books have been heavily illustrated. When I was little I won a "reading award" in my first grade classroom because I always had out this science book. Truth is I was just looking at the pictures and reading the captions. Nevertheless I obviously did learn to read, and I can assure you that seeing pictures as a child ruined my imagination in no way. Think of the vast amounts of data we are presented with every day. There are images, written words, music, speech, on advertisements, street signs, in movies, on television, in books, in classrooms, at home... If having one possibility illustrated (in a broader sense) before you actually stifled human creativity, there would be far fewer inventors, artists, and writers. And if you want proof you can search for "fanfic" and see thousands of young adults (perhaps older adults?) and children writing stories based on their favorite movies and television shows and books, simply because they want to apply their own creativity to the fiction. I found one story, obviously written by a young child, which sought to give a back-story for how pokemon evolved out of present-day animals.
In short, I think the least of your worries should be any new media constraining the imagination.