I've recently finished a manuscript using this template. I've been trying to add a narrow banner type image to the left margin of each page of the journal but to no avail

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Learn LaTeX easily with newest books:
The LaTeX Beginner's Guide: 2nd edition and perfect for students writing a thesis
The LaTeX Cookbook: 2nd edition full of practical examples for mathematics, physics, chemistry, and more
LaTeX Graphics with TikZ: the first book about TikZ for perfect drawings in your LaTeX thesis