PURPOSE: To enhance sharpness of a dye image by adding an organic acid silver salt and an organic polymer binder as well as a white pigment to a precoat layer of an image forming sheet.

CONSTITUTION: A naphthol or phenol derivative of formulae I to IV in which R1 and R2 are H, OH, NH2, 1 to 4 C alkyl, or dialkylamino, X is Cl or Br, n is 1 or 2, and R3 to R5 are H, 1 to 4 alkyl, alkoxy, or dialkyl, alkoxy, or dialkylamino; a sensitizer, such as a sensitizing dye or imidazoles; and a binder are dissolved in a solvent, coated and dried on a support to form a photosensitive sheet. On the other hand, a dispersion fluid of a white pigment, such as TiO2, 1 wt. pt.; a binder 0.2 to 2 wt. pts; organic acid silver 0.01 to 0.5 wt. pt., is coated and dried to form a precoat layer, and an image forming solution containing a complex salt of diazonium compound and ZnCl2, an alkali generator thiourea, etc., and an acid stabilizer (tartaric acid etc.) is coated and dried on the precoat layer to form an image forming sheet. The photosensitive sheet is overlaid by an original, exposed to light, then, overlaid on the imge forming sheet, and developed with a heating roller. The presence of a white pigment permits a sharp and high density image to be formed.