Get ISObuster. Open the img with ISObuster and extract all the files onto your hard drive. You can now use PSicture to scan the files for TIM image files.

Just remember that not all PSX games use TIM graphics. If your TIM search fails to find anything then you are going to have to use some other tool, such as Tile Molester.

Star Ocean 2 is compressed, so even they did use TIM you probably won't find much with standard rip programs.

To be honest, I'm very curious on this as well.  I've always wanted to kind of sprite hack SO2 a bit...but oh well.

Heh.  I've seen people screw up their databases with a program that had only one feature before, so anything that falls under the "no skill needed" category and lets you play God with several different data types, groks the compression and file system and will have it still run on a game console afterwards is quite the accomplishment.  Because not only do you need to pull the data out, you have to get it in a format that another program can edit it (or provide built-in editing, yet another feature), recompress it after any changes, rebuild the disc image, etc.

You've mentioned elsewhere that you're somewhat new to romhacking.  Although editor programs may look simple, they are not trivial tasks.  Good, solid programs take a lot of time.  A rough guestimate would place this one at 1-8 weeks of full-time work for a good developer that already knew all of the data formats involved (we don't), depending on the features implemented.   Most people romhack as a hobby (in their spare time, after work or school), so, assuming that someone takes the bait and picks up the project, it would take a long time for a fully-featured editor that anyone could use to be written.  If you're not likely to put the time into working on it, then it's kind of unfair to ask others.  Some people will simply ignore requests like this, others may respond in flippant or less-than-kind fashion, since a request like this could be considered rude.  People like to help with suggestions and information, but they generally won't do the work for you.

If you are interested in pursuing this yourself, as a starting point I'd suggest you look into some of the documents on compression and/or get a Playstation debugger and find out exactly when/where all of the image data gets loaded.  And you will probably need a hex-editor down the line, too, since no tools exist that I know of for use with the SO2 game internals.