Why don't images in iCloud appear as available in iMovie on IOS?

I want to create a full video on IOS device but use a predetermined asset for an intro screen. I have added a JPEG to my iCloud account formatted to video screen size. I then created a movie project on my phone (6 plus) and clicked "add media " icon, then browse to iCloud and I can see the file, but it isn't selectable. So what am I missing? Is it a file format issue?