Several cognitive factors, including processing speed, memory processes, and meaningful interpretation of stimuli, influence their aesthetic impression. In this study, we investigated whether cognitive load in one task modulates the aesthetic impression of pictures in another task. To manipulate cognitive load, participants remembered a sequence of two numbers (low load) or four numbers (high load) and then rated the aesthetic appearance of pictures on a seven-point scale in terms of their evoked liking, interest, and stimulation. The pictures depicted an everyday scene (non-ambiguous pictures) or were alienated by the inclusion of a semantically incongruous object in the scene (ambiguous pictures). Following the aesthetic rating of the pictures, participants completed a probe number sequence by filling in the missing number. Faster response times and higher percentages correct responses in the low load condition compared to the high load condition ensured the successful manipulation of cognitive load. Processing load increased rated liking and stimulation, but interest was not affected by cognitive load. This load effect was present for both ambiguous and non-ambiguous pictures. Furthermore, participants liked the ambiguous pictures more, found them more stimulating and also rated them as being more interesting than the non-ambiguous pictures. In conclusion, the results suggest that both cognitive load and image ambiguity differentially influence the aesthetic impression of a picture.