we would need to see the whole sentence to understand, but 'to catch the imagination' would mean to capture something, figuratively speaking. "To capture an idea" usually means to successfully convey it, to write or produce something which captures this meaning and conveys it to the audience. But to capture someone's imagination can also mean to stimulate it... so we must see the whole sentence , to be sure

To catch/capture someone's imagination means : to intrigue someone; to interest someone in a lasting way; to stimulate someone's imagination. e.g. The story of Harry Potter has captured the imagination of the world's children.