Methods, systems, and apparatus for processing image content items. In one aspect, a method includes generating an image display environment for a first image content item on an image content item page resource between a first row and a second row of image content items. The user device expands a thumbnail of the image content item from first dimensions to second dimensions, and displays the expanded thumbnail in the image display environment. Concurrently with the thumbnail processing, the user device requests a first image resource referenced by the first image content item, and, upon receipt of the first image resource, generates an adjusted version of the first image resource that meets the second dimensions. The user device then displays the adjusted version of the first image resource in the image display environment in place of the expanded version of the first image content item.