A PDInlineImage is an image whose data is stored in the page description's contents stream instead of being stored as an image resource (see PDImage). PDInlineImage is a subclass of PDGraphic and corresponds to the PDF inline image operator (see Section 4.8.6, In-Line Images, in the PDF Reference).

Inline images generally are used for images with small amounts of data (up to several kilobytes), while image resources are used for large images. The reason for this is that there is a tradeoff between the time needed to access an image resource and the time saved by not having to parse inline image data when display large images is disabled in Acrobat. For small images, the time needed to access an image resource is large compared to the time needed to parse the image data; the opposite is true for large images.