A JPG file is a common image format named after the Joint Photographic Experts Group, who created it. A corrupt file is caused when some of the bits of data that comprise the image are missing or otherwise incorrect. The result is that the image does not open, or it opens blank or distorted. When you encounter a JPG file that appears to be corrupt, try opening it with different programs on your Mac. Often, a file that does not open in one program will open in another. You can then take a screenshot of the image and convert the screenshot into an uncorrupted JPG.
Open a new Finder window by clicking on "Finder" in the dock. Locate the JPG and click on it while holding down the "Control" button.
Select "Open With." A list of suggested programs capable of opening JPG images is displayed.
Choose "Preview," which is Apple's default program for opening image files. Close "Preview" if the file does not display correctly; otherwise, continue to the next Section.
Select each program listed in the "Open With" menu until the image opens correctly. These will include the ColorSync Utility and Safari on all Mac computers. Depending on the software installed, the list will also include graphic programs like Gimp, Firefox, Chrome, Real Player, Adobe products, etc.
Maximise the view window for the image using the program the opens the JPG. If the program includes a zoom function, zoom into the image so that it is as large as possible without distortion.
Press the "Shift", "Command" and "4" keys at the same time. The cursor turns into a cross-haired target symbol.
Move the cursor to the top-left corner of the image. Hold down the mouse button and drag the cross hairs over the image. The selected area of the image is highlighted. Release the mouse when the entire image, and only the image, is highlighted. A camera shutter sound is played.
Click on the "Finder" window, then click "Desktop." A new copy of the image is saved with the file name "Screen shot," followed by the date and time the screen shot was taken.
Double-click the new image if it is not in JPG format. The image is opened with Preview. Click the "File" menu. Select "Save As." Click the "Format" menu and select "JPEG." Rename the file as desired. Click "Save." The image is saved to your desktop with the JPG extension.