static Sprite FromFile(string file, SpriteType type, string atlasId)

string file The filename of the image, an absolute filename, or a filename relative to the assets folder. Supports jpg, png, tga, bmp, psd, gif, hdr, pic.
SpriteType type Should this sprite be atlased, or an individual image? Adding this as an atlased image is better for performance, but will cause the atlas to be rebuilt! Images that take up too much space on the atlas, or might be loaded or unloaded during runtime may be better as Single rather than Atlased!
string atlasId The name of which atlas the sprite should belong to, this is only relevant if the SpriteType is Atlased.
RETURNS: Sprite A Sprite asset, or null if the image failed to load!

Create a sprite from an image file! This loads a Texture from file, and then uses that Texture as the source for the Sprite.