I had trouble posting pictures of my novels' book covers to my Profile Portfolio because my pictures were quite large at about 2000 pixels high and because the Portfolio Add Details page cropped off everything outside the center third of the picture. There is a long thread here that deals with this problem,
but that solution needs Photoshop or a similar program (which I don't use), it recommends reducing the size of the picture to less than 300 pixels which would result in a grainy or blurry low-res picture, and it was originally posted in 2015 and I think that the Portfolio Add Details page has changed since then.
I solved this problem by opening my picture in MS Paint and reducing the size of the picture to 800 pixels in the longest dimension, which is about the largest size this process will work with easily. Then I opened a second window of MS Paint and increased the size of the blank picture to double the dimensions of my new picture; about 1240 pixels wide and 1600 pixels high, and scrolled the blank picture down and to the right until the center of the blank picture was centered in the viewing window. Then I went back to the first Paint window, used Select All to select my picture, copied it, and pasted it into the blank white space in the second Paint window, then just dragged it into the center of the space by eye, and saved it.
You end up with a big picture with a huge white border around it, which allows you to get all of your picture inside the cropping window of the edit picture page of the Add details window when you slide the zoom slider almost all the way to the left, then drag the picture a bit to center it perfectly. It might take a few cycles of Previewing and adjusting to get it exactly centered in the large view.
Anyway, I hope this saves someone else some frustration!