A good reference image is important for relative performance analysis of different image thresholding techniques in a quantitative manner. There exist standard methods for building reference images for document image binarization. However, a gap is found for graphic images referencing. This paper offers six different techniques for building reference images. These may be used for comparing different image thresholding techniques. Experimental results illustrate the relative performance of five different image thresholding methods for the six reference image building methods on a set of ten images taken from the USC-SIPI database. The results would help picking up the right reference image for evaluating binarization techniques. © 2011 Springer-Verlag.