I just got back from a vacation where I took photos with both my
point-and-shoot camera (Canon A540) and my Android phone (Moto X). The camera
uses the filename format IMG_????.JPG while the phone uses the format
IMG_YYYYMMDD_HHMMSS.jpg. This means that the two sets of photos cannot be
easily viewed as one coherent set. To fix this problem, I used exiftool to
bulk rename the camera files to IMG_YYYYMMDD_HHMMSS_????.jpg.
$ sudo aptitude install exiftools
First, I had to fix the timestamp on the camera photos since I forgot to change the timezone on the camera. EXIF timestamps are recorded in local time with no timezone information, so I had to correct the timestamps by adding, in this case, 13 hours.
$ exiftool '-DateTimeOriginal+=0:0:0 13:0:0' ???_????.???
Then, I renamed the files in my desired format, inserting the timestamps
between the IMG\_ prefix and the ????.JPG suffix. I also converted the
suffix to lowercase to be consistent with the Android photos.
$ exiftool '-filename<${FileName;s/_.*//}_${DateTimeOriginal}_${FileName;s/.*_//;tr/A-Z/a-z/}' -d '%Y%m%d_%H%M%S' ???_????.???
Finally, I had to manually adjust the .avi filenames since exiftool cannot write EXIF data for AVI files, and thus cannot adjust the timestamps in the first command. I did this with a simple copy and paste from the corresponding .thm files.