A method of forming an image which comprises subjecting a photographic element comprising a support and at least one photographic layer in which there is image-wise distributed a substance having a catalytic effect to image-wise intensification in the presence of a reducing agent using a solution containing: (1) at least one of hydrogen peroxide and compounds capable of releasing hydrogen peroxide or a halogenite, and (2) at least one nitro-substituted nitrogen-containing heterocyclic compound represented by the following General Formulae (I) and (II); ##STR1## in which R.sub.1 represents hydrogen atom, an alkyl group, SO.sub.3 M or COOM, wherein M represents a hydrogen atom, an alkali metal or ammonium group, X represents nitrogen atom or CR', wherein R' represents a hydrogen atom or a lower alkyl group, and ##STR2## in which R.sub.2 represents hydrogen atom, an alkyl group, SO.sub.3 M or COOM, wherein M represents a hydrogen atom, an alkali metal or an ammonium group and Y represents a hydrogen atom, an alkyl group or CH.sub.2 --S--(CH.sub.2).sub.n --Y' wherein n represents 1 to 3 and Y' represents a hydrogen atom or SO.sub.3 M.