i've been stuck with this problem too lately. You need to rebuild the .pgw file and the .aux.xml file. If your file name didn't change you can just copy back the old file in the folder with the edited .png. Otherwise you'll have to rename them. If this doesn't work you might want to try this.
It will be a two step process. First use the define projection tool in the projection and transformation tool box. Set it to the correct projection. In my case it was geographic WGS84. Use the batch tool to do it quickly. (right click on the tool name) Set your environment variable and it will autofill the paths for you. This will build the .aux.xml
Next you rebuild the .pgw file. I've written a small R script that takes a text file consisting of 9 columns : ID, PATH, FILE, X, Y, ROTATION1, ROTATION2, X_RES, Y_RES, and it builds the .pwg file you need.
liste <- read.table(file="F:/WorkSpace/import_kml.csv", sep=",", header=TRUE)
path = "F:/WorkSpace/files/"
for(i in 1:length(liste){
write(paste(liste[[8]][i],liste[[6]][i],liste[[7]][i],liste[[9]][i],liste[[4]][i],liste[[5]][i], sep= "\n"), file=paste(path, liste[[3]][i], ".pgw", sep=""))
}
So the input file is custom build by hand since I didn't take the time to learn how to parse XML files. It's not long to create using the CMD command in the folder you files are type in dir /s /b *.png for the full file path and dir /b *.png for the file names use ">" to direct the output to a text file. Paste the outputs into a excell spread sheet. Save it as a .csv using the , as a separator. Input the north eastern corner coordinates, (this is the fastidious part) you need to fetch them from your dataframes. Then input the rotation coefficients. If they are perfectly lined up to the north use 0 both times. Then input the x and y resolutions. In my example they are in degree.
input file should look like this
ID,PATH,FILE,X,Y,ROTATION1,ROTATION2,X_RES,Y_RES
1,K:\ASAR_2010_SAR_RGB_2010\files\alaska_20130221.rgb.png,alaska_20130221.rgb,-180.005,72.005,0,0,0.01,-0.01
the script will output a file that looks like that. It will be named the way you need it too.
0.01
0
0
-0.01
-180.005
72.005
It should display correctly after that. Hopefully you won't have to go through all this