You can convert HEIC pictures from the camera to JPEG images when sharing them via Airdrop.
HEIC images is a lossless high compression format. It takes long time to display them and many applications doesn't support them.
JPEG image are compressed and very small. They are very common to many applications and web services.
When you take pictures with the camera the default setting format is HEIC. When you want to share them via Airdrop they are send as HEIC. Many web services and application don't support HEIC at this time. So it will be handy to share your photos from the photo library right away as JPEG.