A general purpose high accuracy dosimeter reader, 80, for determination of a treatment condition, based on comparison of an image of treated dosimeter, 111, with a series of images of pre-treated dosimeter, 114, is disclosed. A dosimeter undergoes noticeable changes, such as a color change upon treatment with certain materials, such as toxic gases and processes, such as ionizing radiation and sterilization is pre-treated. The dosimeter is imaged with an imaging device, 115, such as charge-coupled device camera and images of the dosimeter or the changes, e.g., color change, are stored in an information storage device, 118. In order to determine the treatment condition, the treatment dosimeter is imaged and the image is compared with the series of pre-treated images of the dosimeter using software. The closest match of the treated dosimeter with the pre-treated and pre-imaged dosimeter would indicate the treatment conditions. The process and device can be used for almost any indicating device, process and treatment.