Language teachers are increasingly using image prompts in their composition classes, in keeping with the increasingly visual culture that learners are exposed to. In India as well, teachers use images as writing prompts to help learners practise various kinds of writing. However, there seem to be no specific guidelines or frameworks towards designing images for use as writing prompts, nor any reasoning as to why certain images might work best for this purpose. This research tries to address this, by looking specifically at image prompts in terms of identified content elements (dynamic action, background, foregrounding) and number of images, with the ultimate aim of arriving at a system by which image prompts appropriate for the purpose of eliciting narrative writing from young learners of English can be selected or created. In this experimental study, these image elements have been used to create prompts with specially-controlled features, and the responses of 117 learners from Class 5 of a CBSE school in India, to each of these prompts, have been recorded. Following blind rating by multiple raters, and a close study and qualitative analysis of the responses of different learners, it is concluded that including the content-element parameters of dynamism, a rich background, highlighting of special elements in the foreground, and presenting prompts in sets of 2 images, are ways in which image prompts can be made suited for the purpose of teaching and practice of narrative writing for this age group of learners. A validation study conducted after the main experiment confirms these findings. Additionally, this research also infers two additional points from the analysis of data: that image prompts with such features are particularly helpful in aiding learners to be imaginative and hence produce narratives with diverse themes, and that these prompts are particularly helpful for struggling writers.