You will need a lib which extracts the EXIF data from original and have the possibilitiy to add EXIF data on the new image.
But i think there is no b4a-library available for this. I dont know if the b4a-libs which can convert an jpeg are able to extract/add EXIF data...
After posting my answer i saw this
thread.
Install lib. extract EXIF on original and put them in a variable. convert the image to new size (whatever) and then write EXIF back to the newly created JPG