white dot

i was calling a friend on facetime, while it was ringing i noticed there was a very small white dot in the middle of the screen? so i went to my homescreen to see if it was there but there was no white dot anywhere else. it only appears on my camera app, snapchat, and the facetime camera like when im waiting for someone to pick up and the screen is just me. if i put my finger over my front camera, it disappears. so if i were to cover my front camera with my finger, it disappears. this white dot appears on my snapchat, my normal camera app and facetime when im waiting for the person to pick up. it appears in screenshots, if i try to film it on my camera app, it disappears when i hit the record button. does anyone know what this is?