First and foremost, it should be noted that the app has to run before connecting the smartphone to iPhoto. It works in the background while you take pictures, so when the time comes, iPhoto will find everything already in the right place.
On most devices, the app will auto-configure itself the first time you open it. It will detect the "DCIM Directory" and add the default "Camera" directory to the list of watched directories. Once you see the successful messages on your screen, you can turn on the app and forget about it. If the auto-detection fails, follow this procedure.
DCIM Helper will work on every picture you take after you install and turn it on. If you have old pictures you wish to import in iPhoto, just long-press on the directory name in the watched directories list and a popup will appear. Select your preferred option ("Copy to DCIM..." or "Move to DCIM...") and all existing pictures will be copied (or moved) in the right palce.
In order for iPhoto to recognize your pictures and videos, the
smartphone must be connected through the USB cable with the "USB Mass
Storage", "PTP" or "MTP" options (PTP is better than MTP).
You will notice an external USB disk icon appearing on your Desktop.
You cannot use apps like Android File Transfer for Macintosh because it works in a different way and opens a special Finder window that iPhoto will not recognize (another Google failure).
In the rare event that auto-detection doesn't recognize your DCIM folder, you can do a manual configuration. It requires some steps which will be detailed here. Some of them are not strictly required, their purpuse is to be sure of the configuration.
Now you can add the folder which contains your pictures in the list of "Watched directories". Turn ON the app, take some pictures and connect back the smartphone to iPhoto. It will now show your pictures!
If you had to use this procedure, please send me an email with the full text that appears under "DCIM directory" so that I may update the auto-detection for new users with your same device.
Starting with Android 4.1 "Jelly Bean", Google changed the behavior of the stock Camera app in a way that breaks DCIM Helper and any other app that uses pictures from the Camera as soon as they are taken.
If you are running Android 4.1 "Jelly Bean" (or above) on a Google-branded device (e.g.: Samsung Nexus S, Samsung Galaxy Nexus, LG Nexus 4, …) or an aftermarket ROM based on AOSP (e.g.: CyanogenMod, AOKP, …) or if you know you're using the Android Camera app, then enable the "JellyBean+ Camera hack" in the options. This option is hidden on devices running Android 4.0 "Ice Cream Sandwich" or below.
Sure you can! You can either contact me through the app's own G+ page, my own G+ profile or the forum page on the famous XDA-Developers forum. You are welcome to post a comment and rating on the Play Store, but since it is not yet possible to reply to such comments, I won't be able to reply you there.