Last three decades, early cancer detection and researches on early detection solutions play vital role for human health. Computed tomography images (CT) are widely used in radiotherapy planning because they provide electronic densities of tissues of interest which are mandatory to a correct dose computation. Furthermore, the good spatial resolution and soft/hard tissues contrast allow precise target delineation. Also, CT techniques are preferred compared to X-Ray and MRI images. Image processing techniques have started to become popular in use of CT images. In this study, image pre-processing, image erosion, median filtering, thresholding and feature extraction of image processing techniques are applied on CT images in detail. The aim of this study is to develop an image processing algorithm for lung cancer detection on CT Images.