What is a thumbnail or media preview?¶

A thumbnail or media preview is an application-generated representation used to display content quickly. It can help identify missing media, but it is not the complete original file.

A derivative has its own properties¶

The application may resize, crop or compress an image, select one frame from a video, render one page of a document or fetch summary material for a link. It can store that derivative separately from the source attachment.

The preview may therefore survive after the original is deleted, moved or never fully downloaded. Its dimensions, quality and metadata relate to the generated representation and may not describe the source file's creation or contents in full.

State exactly what was recovered¶

Preserve the preview in its native location with its dimensions, timestamps, associated message or attachment identifier and application context. Search downloads, caches, galleries, backups, linked endpoints and recipient devices for the original.

A recognisable preview can support that the application processed or displayed a representation of particular content. It cannot establish that the full file was present, that every part looked the same, or that a person deliberately viewed it. Preview generation may be automatic.

Reports and exhibits should label a thumbnail as a thumbnail rather than silently presenting it as the original attachment.