Put them in a folder (Preferably some subfolder of #Bitmaps\Tiles), then go to Tools --> Import Bitmap Fill Styles. This will create the different fill style resolutions used by CC3, as well as import them as fill styles into the current map. The name of the fill style will match the original filename.
See part 6 of this tutorial for more on creating fill styles. Don't forget to save as a template when done.
Note that the Import Bitmap Fill Styles way imports all the pngs from the target folder, so you'll perhaps want to limit the number of files in a very specific folder.
Comments
Is there a limit to the size of the image H*W and DPI?
Note that the Import Bitmap Fill Styles way imports all the pngs from the target folder, so you'll perhaps want to limit the number of files in a very specific folder.