In this article, we propose two novel histogram-based techniques that are robust to the changes in image illumination levels. Given a query image and an image database, current histogram-based techniques retrieve similar images acquired under similar illumination levels. However, these techniques fail when images are acquired under varying illumination conditions. First, we propose employing moments of the image histogram that are invariant to scaling and translation of image gray levels. Second, we propose comparing the parameters of histograms of the wavelet subbands for indexing. These parameters are modified appropriately to counter the effect of changes in illumination. The proposed techniques can be combined to further improve the indexing efficiency. The techniques are computationally inexpensive and can also be easily integrated within a wavelet-based image coder.