Which file format supports image layers?

The Portable Network Graphics (PNG) format supports image layers by allowing for transparency and a much broader range of color depths compared to formats like JPEG or BMP. One of the key features of PNG is its support for alpha channels, which enables varying degrees of transparency. This allows images to be layered without the need for a solid background, making it ideal for web graphics where images often need to blend seamlessly with various backgrounds.

While GIF also supports transparency, it is limited to a single color set as transparent rather than providing the nuanced transparency levels found in PNG. JPEG and BMP formats do not support layers; JPEG does not allow for any transparency and is primarily used for photographs, while BMP lacks compression and is generally used for simple images without any layer or transparency support.

Thus, PNG stands out as the versatile format that can effectively handle images requiring layers and advanced transparency options, making it the correct answer for this question regarding file formats that support image layers.