no community forum available for Portfolio, thought I'd give this forum a shot.
when viewing verticle images all of the thumbnails in the gallery are visible as ghost like images to the left and right of the main image being viewed.
no problem with horizontal images because they cover the entire viewing area.
I'm having trouble envisioning this. Also it's unclear to me if you're talking about Cover Images, Photo Grids or regular images.
Photo Grid Module
Thank you for responding to me inqury Nancy. A member of the Portfolio support staff solved my problem and all is well now.
The fix involved changing the settings in Light Box for images under site settings.
No answer, not enough experience with 'Portfolio' to suggest a fix, but I understand the OP is referring to the background when enlarging one (vertical) photo to view in Portfolio- See my example: the thumbnails show as feint background.
Screen-clip from https://cullen-r0b.myportfolio.com/america-revisit-selects
that's exactly correct. no longer have that problem.
After re-reading your post, maybe you're asking about the optional Lightbox image viewer which opens inside a modal window, superimposed over the page. See link below for details.
yes, that is exactly what Portfolio support had me do to correct problem.