The GIMP photo editing software includes the ability to convert your JPEG image files into many other file types, including a TIFF file.

For a quicker photo-to-sketch conversion, you might want to try out previously-mentioned software Photo to Sketch.

Pick out a photo and open it in GIMP. Try to avoid overly cluttered backgrounds, as they end up difficult to discern when converted to a sketch. Navigate to Filters>Edge-Detect>Sobel.