Photos app shows only some photos on SD card

I'm using the Photos app on my MacBook Air to import photos. But the Photos app is only showing a portion of all of the photos on my SD card. For example, looking at my SD card in the Photos App, it shows that I took 51 photos on 1st Nov. But looking at my SD card with Finder, it shows that I took 84 photos. There are definitely some photos on my SD card that the Photos App isn't picking up, despite them all being the same file type and no huge difference in sizes from each other. Help!