The current method for displaying images in a Google search is a row of four similarly sized images. Maybe what you want shows up in the line-up, maybe it doesn’t. The only way to know for sure is to click through to the image results page.
The new method will show one large image, with a two rows of smaller images to the side. With more images available it will be easier to determine if you’ve got the right results from your search.
The new format is expected to be available within the next twenty-four hours.