When you take a capture via the Snapshot button on your Board, it appears as a slideshow in the Views > Captures menus.
The slideshow of the captures taken is displayed:
You can use the left and right arrows to switch between the snapshots, and the binto discard the one displayed.
Click on the capture to be downloaded to view it in full size:
The arrow for downloading the capture is at the very bottom left.
You can retrieve all captures at once by downloading the data from the Board: Download Activity Data