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.
In iOS 11 you can save images as HEIC files instead of JPEG files, which require considerably less storage than JPEG files without sacrificing image quality. If an iPhone user shares a HEIC image with a non-iPhone user or to a social site, the HEIC image is automatically converted to a JPEG image.