Picture Resolution for Nikon D5100?

I have a Nikon D5100 DSLR camera. When I compare the image specs between pictures I took a month ago and pictures I took just today, I noticed the following difference:

- Pictures taken a month ago: 4737 pixels x 3158 pixels, 789 dpi
- Pictures taken today: 4737 pixels x 3158 pixels, 300 dpi

The image quality settings have never been changed - They have always been set to "fine".

Are the image resolution the same for both pictures? The number of pixels seems the same, but dpi (dot per inch) is different. Why is that?

Yes, the image resolution for both pix is the same, 4737x3158 pixels.

dpi is purely a printer spec. You can instruct your printer to print at various dpi, such as 75dpi, 150dpi, 300dpi, 600dpi, 1200dpi. You also instruct it to print at various sizes, such as 4x6. If you do the math for printing one of your pix at 4x6, 300dpi, you'll discover it is going to use only 1200x1800 dpi. So what to do with the extra pix? It just interpolates and throws away what's left over.So, dpi has nothing to do with the resolution of the photo.

How did the dpi change? I can only guess. Maybe you printed directly from the camera to a printer.