Studies by Oxford revealed what people "Like":
Images depicting objects (e.g. food, possessions) were significantly more likely to be Liked than images depicting faces.
When asked to rank the reasons they Liked an image:
64.1% of participants selected, ‘The image was visually appealing’, as their top choice
‘The image was similar to one that I might take’ (12.8%)
‘The image depicted an activity that I enjoy’ (10.3%)
‘The image was funny’ (5.1%)
‘The image contained one or more attractive people’ (2.6%) or other
When asked whether they thought about liking an image before selecting, or if they went with their gut instinct, 63.4% responded ‘Gut instinct’ and 36.6% responded, ‘thought about it’.