PowerPoint compress images

Well, you could reduce the size of the images by saving them in a lower resolution, or different file format. That option depends on your skill with an application like Photoshop or similar.

COMPRESS IMAGES IN POWERPOINT
Click on any picture in your presentation.
You should see the "Pictures Toolbar". If you do not, check the "View"→"Toolbars"→"Picture" option from the menus. Click on the "Compress Pictures" icon as shown.

You will see the "Compress Pictures Dialog" box. Select "All pictures in document". If you are sending the file out for screen viewing and review only, then select the "Web/Screen" option and both checkboxes, "Compress pictures" and "Delete cropped areas of pictures".

Use "File"→"Save as..." menu item to save your presentation with a new file name, adding the words "For Review", "For Viewing", "For Printing", or something similar. You should keep your original Powerpoint file, or at least the original pictures, in case you need to edit the pictures again.

A six megabyte file can become 200 KB when pictures are compressed for the web, and 500 KB when compressed for printing. That represents an order of magnitude reduction in file size. Remember, by compressing the presentation, you lose the cropped parts of the pictures and the fine detail of the pictures. If you need those again, make sure to save the original presentation or the original pictures.