Where is my apple account picture stored on my mac?
I don't know where it's stored, but I know how you can find it...

Open Contacts, and navigate to your card, then click on the image. A box will appear with four options in the sidebar. Click "Recents", and one of the images it displays will be the one you want. Next, click on this image to set it as your Contacts image, the click "Done". Now open a new Finder window, then press Shift-Command-G. Copy the following path into the dialog box that appears: ~/Library/Application Support/AddressBook/Sources/ Click "Go". You will arrive in a folder which contains a number of other cryptically named folders. One at a time, open each folder, then Click the "Date Modified" header in the Finder window to sort by date. In one of these folders, date modified today, you will find the image. It will actually be there twice. There will be a low res version, and a slightly higher res version. (The reason it will be date modified today, not back whenever you took the photo, is because this is the folder for "Contacts" images, not the original folder.)