Imagery training has been shown to improve reading comprehension. Recent research has also shown that the quality of visual mental imagery used is important for reading comprehension. A review of literature shows that there has been relatively little detailed research on the quality of imagery used by learners, especially in the case of students learning English as a foreign language (EFL). This study was designed to examine the influence of image quality on reading comprehension in EFL students, comparing the effects of training in the use of a focused, constrained imagery relative to that of a more standard form of visual mental imagery training. The study also examined the impact of individual differences such as gender, ability to make images, working memory capacity, and motivational beliefs on the training outcome. The findings provide evidence that constrained imagery strategy training helped EFL learners improve reading comprehension. Female participants showed higher comprehension performance than males. Other individual difference variables did not emerge as having a significant impact on change in reading comprehension performance over time.