A method for forming an image by a positive resist process comprises:(1) exposing imagewise to actinic radiation a photoresist composition comprising:(a) a film-forming organic material having at least one substituted benzoin group of formula: ##STR1## where R.sup.1 denotes a hydrogen atom, an alkyl, cycloalkyl, cycloalkylalkyl, or aralkyl group or a group --(CH.sub.2).sub.b X; R.sup.2 denotes a hydrogen atom or an alkyl, cycloalkyl, cycloalkylalkyl, aryl or aralkyl group; R.sup.3 denotes a halogen atom or an alkyl, alkoxy, cycloalkyl, cycloalkylalkyl or phenyl group; X denotes a halogen atom, an alkoxy group, a phenoxy group, a group --COOR.sup.4 or a group --OOCR.sup.4, where R.sup.4 denotes an alkyl group; a denotes zero or 1; b denotes an integer of from 1 to 4; m and n each denote zero or 1, the sum of m+n being 1; p and q each denote zero or 1, the sum of p+q being 1; and c and d each denote zero or an integer of from 1 to 3; and(b) a compound which is polymerizable under the influence of a free radical catalyst to form a higher molecular weight material which is more soluble in a developer than the composition prior to exposure, so that the solubility of the composition in a developer is increased in the exposed portion; and(2) treating the composition with a developer to remove the exposed portion.