Yeah, I agree with admirable, use iPad's own Photos, and use the slideshow. Actually....
What I do is save a pick of my graphic design work on CorelDRAW and saved them in JPG format, then place the JPGs into a folder of its own (folders on PC when sync to iPad becomes albums on iPad), rename the filenames to numbers to ensure they are in right order, and sync it to iPad. I also pick any photos I need to show, and copy some into a folder of its own too, also number the filenames to ensure they're in order I want.
It's a lot easier. Open the iPhotos app, tap the album you want to show, and hand it over, they can just swip any as they like. Downloaded apps may have its own ways of displaying the next image, for example, what if the app you downloaded have a button you need to tap on to view the next page, but whoever you're showing is more used to swipping images? Whoever you wish to show your photos to, supposing they do have their own iPad, iPhone, iPod Touch, or if not having their own but did try out any of those iDevices (trying out a friend's iPad for example) so they are familiar with iPhotos on iOS, iPad's own photos, but are not familar with any portfolio apps you downloaded.