Decide what appears different
You have a saved copy of a public diagram, but the image now visible on its Wikimedia page seems different. Identify the difference you are investigating: the image pixels, a caption, a credit or the surrounding description. These objects do not necessarily change together.
Keep your reference copy and its known source address. Do not assume that an identical filename means the current file bytes are the same as the version you saved earlier.
Open the history for the right object
MediaWiki’s help distinguishes the file page’s displayed image, description, file history, usage and metadata. It says File history includes upload dates and previous uploaded versions, while the page’s edit history records text and description changes. Source
If you are checking a cropped border or corrected diagram label, inspect File history and the relevant accessible image versions. If you are checking a changed credit or explanation, inspect the description’s revision history. Record both when the question involves both objects.
Compare without assigning a broader chronology
| Record | What it helps establish | What it does not establish alone |
|---|---|---|
| File upload time | When that version entered this file history | When the image was first created anywhere |
| Description revision | How the page text changed | That the image pixels changed at the same time |
| Upload comment | The uploader’s explanation of the change | Independent confirmation of that explanation |
| Actual image version | What the inspected copy displays | The full context of every later reuse |
For an illustrative diagram, a later upload might replace a misspelled label while the description remains unchanged. Save the version showing the label relevant to your comparison. Do not rewrite the earlier image’s text in your notes to match the corrected copy.
Check whether the file is shared from another wiki
MediaWiki notes that a local file description can include information from a shared wiki such as Wikimedia Commons. Source Read the notice and follow the actual shared-source link when that is where the file history lives.
A file displayed in several language editions can still be one shared underlying image. Do not count each display as an independent original or assume that a local description contains every version record.
Save a reproducible comparison
Record the file page, the specific history entry or image address you opened, the visible difference and your access date. If an older version cannot be viewed, leave that comparison incomplete rather than reconstructing its appearance from the upload comment.
The Commons credit guide covers the separate task of reading attribution. The modified-image guide helps compare copies found elsewhere. Version history explains the local sequence you inspected; it does not by itself settle authorship, rights or the truth of a diagram’s subject matter.