Pictures stored more than once
Safe. On by default.
Stores each repeated picture once.
Why it takes space
Insert the same picture several times in Excel and it stores the picture once, with each use pointing at that copy. Code libraries, and some ways of copying, write one copy per use instead.
Each extra copy costs the full size of the picture, and Excel keeps a picture at its original resolution however small it is drawn.
What ShrinkExcel does
ShrinkExcel groups pictures whose bytes and file type match exactly. It keeps the first copy in each group, points every use at it, and removes the rest.
A drawing names its picture through an id, and the ids do not change. Only the copy each id points at changes, so no drawing or sheet is rewritten.
No picture is resized, cropped or recompressed. Two pictures that look alike but differ by a single byte both stay.
What you will notice
Nothing. Every use shows a copy with the same bytes it showed before, at the same size and in the same place.
In a check in Excel for Mac on 2026-09-24, a workbook shrunk this way opened with every picture in place and the same cells as the original.
Doing it in Excel
Excel has no command that merges identical copies of a picture. Compress Pictures, on the Picture Format tab, lowers resolution and deletes cropped areas instead, which changes the pictures.
It runs on every workbook you drop on the front page, unless you switch it off under Advanced settings.