Inaccurate data in scientific papers can result from honest error or intentional falsification. This study attempted to determine the percentage of published papers containing inappropriate image duplication, a specific type of inaccurate data. The images from a total of 20,621 papers in 40 scientific journals from 1995-2014 were visually screened. Overall, 3.8% of published papers contained problematic figures, with at least half exhibiting features suggestive of deliberate manipulation. The prevalence of papers with problematic images rose markedly during the past decade. Additional papers written by authors of papers with problematic images had an increased likelihood of containing problematic images as well. As this analysis focused only on one type of data, it is likely that the actual prevalence of inaccurate data in the published literature is higher. The marked variation in the frequency of problematic images among journals suggest that journal practices, such as pre-publication image screening, influence the quality of the scientific literature.