A computer-implemented method comprising: identifying, by a computing system, one or more content items for potential presentation to a user of a client computing device operated by the user; transmitting, by the computing system, to the client computing device information pertaining to the one or more content items, wherein this information includes identifying information for the one or more content items and likelihood of consumption values for each of the one or more content items, the likelihood of consumption value being indicative of a likelihood that the user will view the content item; receiving, by the computing system, from the client computing device, a request for a first portion of one of the one or more content items, wherein the content item is an image encoded in a progressive JPEG format and is divided into a plurality of segments, the first portion comprises a subset of the plurality of segments, and the client computing device is configured to determine the first portion of the content item based on the likelihood of consumption value associated with the content item, such that the first portion represents a relatively small portion of the content item if the content item has a relatively low likelihood of consumption and a relatively large portion of the content item if the content item has a relatively high likelihood of consumption; and transmitting, by the computing system, the content item to the client computing device, wherein the first portion of the content item is prefetched by the client computing device and a remaining portion of the content item is provided to the client computing device at a later time. identifying, by a computing system, one or more content items for potential presentation to a user of a client computing device operated by the user; transmitting, by the computing system, to the client computing device information pertaining to the one or more content items, wherein this information includes identifying information for the one or more content items and likelihood of consumption values for each of the one or more content items, the likelihood of consumption value being indicative of a likelihood that the user will view the content item; receiving, by the computing system, from the client computing device, a request for a first portion of one of the one or more content items, wherein the content item is an image encoded in a progressive JPEG format and is divided into a plurality of segments, the first portion comprises a subset of the plurality of segments, and the client computing device is configured to determine the first portion of the content item based on the likelihood of consumption value associated with the content item, such that the first portion represents a relatively small portion of the content item if the content item has a relatively low likelihood of consumption and a relatively large portion of the content item if the content item has a relatively high likelihood of consumption; and the content item is an image encoded in a progressive JPEG format and is divided into a plurality of segments, the first portion comprises a subset of the plurality of segments, and the client computing device is configured to determine the first portion of the content item based on the likelihood of consumption value associated with the content item, such that the first portion represents a relatively small portion of the content item if the content item has a relatively low likelihood of consumption and a relatively large portion of the content item if the content item has a relatively high likelihood of consumption; and transmitting, by the computing system, the content item to the client computing device, wherein the first portion of the content item is prefetched by the client computing device and a remaining portion of the content item is provided to the client computing device at a later time.