A light-sensitive diazonium group-containing polycondensation product of a diazonium salt corresponding to the general formula ##STR1## wherein R.sup.1, R.sup.2, and R.sup.3 denote hydrogen atoms, halogen atoms, alkyl groups having 1 to 3 carbon atoms or alkoxy groups having 1 to 6 carbon atoms, and X denotes the anion of the diazonium salt, and an aldehyde selected from the group consisting of dialdehydes, acetals of dialdehyde hydrates, and esters of dialdehyde hydrates, a process for producin...