what is "Preview" on the dock?

Preview is the application normally used to read PDF files, look at image files, etc. When you ciick on the Dock icon you should see its menu bar appear at the top of the screen. You can then select Quit from the File menu. Or you can click and hold or CTRL-click or RIGHT-click on the Dock icon and the contextual menu will appear. There will be a Quit or Force Quit option you can choose to quit the program.

If it is always on, it may be included as a login item. If you don't want it to be, you can go to system preferences, select accounts, click on your user account and go to login items. If preview is there, then you can select it, click on the "-" tab, and it will no longer open when you start your computer up.

It will open any time you select a document to be read by preview. For example, if pdfs are read by preview as a default, rather than adobe reader or acrobat, then any time you try to open a pdf file, it will open in preview. Same for images.

However, the Preview app icon is not "a guy holding a camera lens", so something else has obviously happened here.

If you Ctrl-click (or right-click) the icon in the dock, and select "Show in Finder", what does it show you?

preview is an App. which enables you to look at PDFS and Pictures etc... =]

Preview is my first choice for viewing and first level manipulation of jpeg files. Loads much faster than Adobe Elements or iPhoto and is easier to use in viewing full screen renditions.

Don Rieg