Consider something ‘playing card’ size so that an individual can comfortably spread out and see a larger collection of images in front of them. Also consider activities which are self-working.
Consider something ‘post card’ or A5 size so that others can see images chosen by individuals and generate some group dialogue.
Consider something A4 or US Letter size so that others can see images chosen by individuals and generate some group dialogue. Consider placing images for viewing on floor for very large groups and have people walk amongst the images. Or break people into subgroups of up to 6 and use the Small group image suggestions.