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 is a new file format on iOS 11 devices. If you want to converter iOS HEIC photos to JPG format, then there are two options out there. You can convert HEIC to JPG online for free or use HEIC to JPG Converter on Windows.