Statistical significance considers the first and third of these concerns. The middle one, bias, cannot be detected by mathematical deductive logic: it needs detailed information on the way the sample was chosen. This is dealt with in the notes on bias.
A HEIC file is a raster image saved in the High Efficiency Image Format (HEIF), a lossy compressed format. It may contain still images, image collections, image bursts, or image sequences, along with metadata that describes each image. HEIC files may also appear as .HEIF files.
HEIC was developed by Apple and it is the default file type for photos being taken on latest iOS 11 devices, such as iPhone X, iPhone 8 or iPhone 8 Plus. When connecting those devcies to a computer, you will see the photos are ended up with heic.