Although Mathew Brady admitted in his own account that he unable to take any pictures of this first battle...there is one picture in the Brady Handy Collection labeled "Confederate Dead at Matthews Hill"

see https://en.wikipedia.org/wiki/Mathew_Brady#/media/File:Confederate_dead_on_Matthews_Hill,_Bull_Run_(i.e._Antietam)_LCCN2012647848.jpg

There is reason to doubt this caption:
Brady own account;
The "Dead" men are actually Union soldiers wearing greatcoats.
Their poses are just a bit too contrived.
A previous photograph showing the "Dead" men very much alive and posing in the act of Firing Rifles was found by Historian William Frassanito.[ See William Frassanito's "Antietam" pp.30-31]
LAStly there is a third picture of the greatcoated Federal soldiers
at a Picket Post..Very much alive...!
https://en.wikipedia.org/wiki/Mathew_Brady#/media/File:Pickets_cooking_their_rations._Reserve_picket_fort_near_Fredericksburg,_December_9,_1862,_by_Taylor_&_Huntington.jpg

My own theroy is that 1861-1862 a northern photographer was taken photographs on a Union encampment--Picture No 1 of the Pickets cooking; then he got the idea to have four of them posing in the act of "Firing" their Guns {Frassanito} then he pictures them "playing dead." {When I wrote to a NPS Historian on how these pictures were "Linked" he generally agreed..but added that the Picket picture was apparently not taken near Fredericksburg...