This might be because you have activated the password protection feature via the "Add-ons" page.
The Add-ons section allows you to choose which areas of your site to password protect. Once logged in to the admin area click on the "Add-ons" option (the one that looks like a puzzle) located on your admin tool bar (the black navigation bar at the top of your screen), scroll down to find the section(s) you wish to choose the password protection option for.
If you wish to keep the password protection feature on you can share the password with trusted club members. The password you have chosen is also displayed in the "Settings" area (which can also be found on your admin tool bar).
Alternatively, you may have password protected the images via the main 'Settings' page. See image below.