Thumbnails are ideally implemented on web pages as separate, smaller copies of the original image, in part because one purpose of a thumbnail image on a web page is to reduce [[Bandwidth (computing)|bandwidth]] and download time. Some web designers produce thumbnails with [[HTML element|HTML]] or client-side scripting that makes the user's browser shrink the picture, rather than use a smaller copy of the image. This results in no saved bandwidth, and the visual quality of browser resizing is usually less than ideal.
Displaying a significant part of the picture instead of the full frame can allow the use of a smaller thumbnail while maintaining recognizability. For example, when thumbnailing a full-body [[portrait]] of a person, it may be better to show the face slightly reduced than an indistinct figure. However, this may mislead the viewer about what the image contains, so is more suited to artistic presentations than searching or catalogue browsing.