This empirical study investigates the effect of online textual, pictorial, and textual pictorial glosses on the incidental vocabulary learning of 90 adult elementary Iranian EFL learners. The participants were selected from a pool of 140 volunteers based on their performance on an English placement test as well as a knowledge test of the target words in the study. Afterward, they were randomly assigned to 3 groups of 30 and subsequently exposed to the research treatment. During 3 sessions of instruction, 5 computerized reading texts including 25 target words were studied. The participants read the texts for comprehension and, at the same time, were able to consult the glosses attached to the target words. Having read each text under each research condition, the participants were tested on their incidental vocabulary learning through two research instruments, word and picture recognition tests. The results of a one-way ANOVA analysis of the data indicate that a combination of text and still images resulted in significantly better incidental vocabulary learning, confirming the Dual-coding Theory (Paivio, 1971, 1990). (Contains 2 figures and 2 tables.)