How to Open a JPEG Picture With an iMac
The JPEG image format is a compressed format, popular for the distribution of photos on the Internet because of its combination of high quality and relatively small file sizes. If you own an iMac, you have several ways to open JPEG pictures on your computer. You can open and view a JPEG image on an iMac by double clicking it, dragging into an open Safari window, or importing it into your iPhoto library.
Double click the JPEG file. The image opens in the Mac Image Preview utility. If you would rather see the image in a Web browser, perform Step 2 instead.
Launch Safari from the Applications menu or from the dock.
Click and hold on the JPEG file that you would like to open, then move the mouse cursor to the open Safari window. This "drags" the file icon along with the mouse cursor.
Release the mouse button while holding the JPEG file over the Safari window. The JPEG picture opens in Safari. If you would rather import the image into your iTunes library so it is on the iMac permanently, perform Step 5 instead.
Launch iPhoto from the Applications menu or from the dock.
Click on the JPEG picture and drag it to the "Library" section of the iPhoto window. A green plus sign appears over the mouse cursor. Release the mouse button to import the picture into your iPhoto library.
Double click the picture in your iPhoto library to view a larger version.
Drag the original copy of the JPEG photo to the Trash if you like. The imported picture remains in the iPhoto library.