How can I encrypt photo files on my iPhone 3GS or iPhone 4 with a password and without any quality loss?
Is there an app for that?
I'm now using CryptMyPic, as it's the simplest and most secure I've found so far.
There are several apps for that. My Eyes Only™ Photo is one that gets good reviews.
Private Pal may do what you need, and more, with full encryption on text and large files, flexibility to create customized folders with own icons. Also supports preview for doc, xls, pdf, jpg, mp4, etc. Bulk import photos, search, fav and recent list, multi-account ...
Ben the Bodyguard is an app that buzzed for a while. It's now available and can encrypt photos, but also contacts, passwords, notes (and probably more).
This doesn't meet your criteria but it may be of interest to others searching on the topic:
SpyPix allows you disguise one photo within another using steganography. This is by definition a lossy process. It's not encryption as we generally define it, but it's a reasonably safe way to "hide" a private photo in your photo libary or to share a private picture (or secret message) with a confidante.
At the very least, it's fun to play with.
I have used iDiscrete for some time. It generally works well with regard to photo security although I could not find a specific call out as to whether is encrypts the photo's once secured. From their website:
For less than the price of a cup of coffee, iDiscrete is the most fully featured privacy application available for the iPhone. Rather than requiring a suspicious looking password, iDiscrete employs its patent-pending Touch Sequence Protection™. This works by bringing up a nondescript "Loading" screen upon entry to the application, which registers touch input in 8 discrete locations. The user has predefined their desired Touch Sequence, which can be as simple or as complicated as they wish. The Loading screen will only grant access to iDiscrete if the correct Touch Sequence is entered. Otherwise, when the Touch Sequence Timeout expires without receiving the correct sequence, the app will boot to a generic-looking text entry interface.
The security system is simple and straightforward to setup. A brief overview of the product can bee seen in this video. The compelling feature for me is that the application support multiple file times and is not just limited to pictures:
The application is priced reasonably at $2.99 in the Apple APP store: direct link