I typically set my image resolution for the web at 72 pixels/inch. Does Google look at image resolution as a ranking signal? Should I save my images at higher resolutions or does it not matter? The higher resolution images mean larger k sizes but I was not sure about what is acceptable.
Additional links I found helpful:
http://youtu.be/h2Zaj0CAUoU (the most helpful)
Different Search Engines have different criteria/Algo. For Image search but as far as Google image search is concerned
I haven’t seen any such evidence that the resolution matters for a general image search, rather markup techniques (proper naming, right alt attribute ) plays a vital role.
But the resolution/size of your image will matter when the user filters the image results through sizes Large, Medium Icon etc.
There is a lot of info about optimizing images for Google search, Just use Google itself to find a more detailed answer, I found few links below pretty helpful though not specific to Google but can give you fair idea about the whole process, you might want to have a look at these: