Before the recent changes, clicking the listed resolution of an images would result in a search for alternate sources of the image, listed by resolution.
It's still possible to get these results by copying the image URL, going to images.google.com choosing search by image, picking URL and pasting in the source you found.
With this (first result for an image search for "car") as an example URL: https://www.cstatic-images.com/stock/379x253/15/img-1276321340-1509471668915.jpg
Before the recent changes, clicking the listed resolution of an images would result in a search for alternate sources of the image, listed by resolution. It's still possible to get these results by copying the image URL, going to images.google.com choosing search by image, picking URL and pasting in the source you found. With this (first result for an image search for "car") as an example URL: https://www.cstatic-images.com/stock/379x253/15/img-1276321340-1509471668915.jpg
This would be the search URL showing alternate sizes (Which doesn't look very helpful to me): https://www.google.com/search?safe=off&hl=en&q=car&tbm=isch&tbs=simg:CAQSlwEJVyVSPBXpYsYaiwELEKjU2AQaBAgVCAgMCxCwjKcIGmIKYAgDEijzDfYN8g30Dd0E9Q3OBPEN-Q3fBMoyvTLhILwyyzLJMroywzK1P84yGjDoZ8pA9mX7Mcv7BXxuBq7OhozZf739GJrh9kmrbxrUZQ39zo7EXosNGWkgra33MnMgBAwLEI6u_1ggaCgoICAESBAUYHhsM&sa=X&ved=0ahUKEwiarKHB6KzZAhUD0WMKHfNcAmUQ2A4IJygB&biw=1920&bih=974