I just noticed that Google is testing image filters in Universal Search SERP. It seems like this filter will appear based on the search intent.
If you are searching for ‘Meghan Markle’, it appears on Page 2. But Google shows the filter in Page 1 for ‘Long black dress’ as its intent for ‘image results are far stronger than the previous case.
Image Filters in Google Universal Search – Page 2 for Meghan Markle
Image Filters in Google Universal Search – Page 1 for Long Black Dress
Using the image filter without going to the Images tab would drive higher traffic to the images. This makes the case of optimising the images even higher priority now.