Fluorescence techniques have shown great potential for detecting animal feces on foods. A recently developed field portable multispectral fluorescence imaging system was used to acquire steady-state fluorescence images of feces contaminated apples. Twenty Red Delicious apples encompassing natural color variation were artificially contaminated with dairy cow feces to create five fecal contamination spots on each apple. The feces spots were not clearly visible to the human eye. Multispectral fluorescence images, with wavebands centered at the red emission peaks of cow feces and apples, in addition to blue and green bands, were evaluated to determine an optimal red band for detection of feces contamination spots on apples. The results show that fluorescence emission bands at 670nm provided the greatest potential for the detection of feces contamination on apples. In addition, investigation of multispectral fusion methods indicated that band ratio image of 670nm to 450nm or 550nm improve sensitivity of detection. Two-band ratios along with the use of unsupervised histogram-based thresholding allowed detection of cow feces contaminations on apples regardless of apple colorations with a 100% success rate. (c) 2004 Elsevier Ltd. All rights reserved.