Issues with uploading files to imagej on Chromeboook

I am a university student trying to use imagej on a Chromebook to create a scale using an image of a graticule scale so i can measure different parts of fish- but when I try to drag the image over it does not open and when I try to do File-> Open it only allows me access to my imagej software files- NONE of my own laptop files/images documents- does anyone know how to fix this or have any advice please