I put the flag in a blender. Oops.
From the comment:
$ exiftool chall.png
Comment : Q3JlYXRlZCB3aXRoIEdJTVA=
$ echo "Q3JlYXRlZCB3aXRoIEdJTVA=" | base64 -d
Created with GIMP
We know that it is created with GIMP. After trying the effects in GIMP, we find the correct one and reverse the effect:
Flag: K17{tw1st_0f_f4t3}
.