Help with a image in a gui

I have an image that I only want to show up if they have a specific item in inventory. I want this sword called "Jeblin Sword" to allow another item (Name irrelevant) should open a gui (kind of like a book) that should display an image of cursive writing that is a code to continue my story. I'm not sure how to make a procedure so that this image of text only shows up when I have this sword in the inventory. I still want the GUI to open with the item but go without the large body of text, as like a secret message imprinted in the GUI. Please help! lol