upload covering image into (hidden) album

view the cover image, copy the image URL under the image.

at your target album, click "edit summary"

click the "insert image" button, enter the image URL at the insert image window. Click "OK"

if you want your visits can jump to other location / album by click the cover image, select the image by click it once.

click the "insert link" button, enter the target link at the insert link window. Finally, save your work.