At this point I think the cat is out of the bag. Yes you could rerelease with that patch rolled back, or you could rerelease with an incremented minor number as is to indicate the change. However my suggestion would be to email ros-users and notify them of the ABI change and recommend they make sure to recompile anything they have built depending on image_transport when they install the update.
We generally try to stay ABI compatible in our releases but we don't make guarantees of ABI compatibility. On the buildfarm we painstakingly track all dependencies and rebuild every downstream package making the assumption that every release breaks ABI. It is a lot of time and effort to build all those packages, but until
we have ABI versioning we cannot do much better. (We talked about ABI versioning in the REP
127 discussions but ended up leaving it out due to not being able to
reach a consensus on it
http://www.ros.org/reps/rep-0127.html)
In general my recommendation is to recompile anytime you apt-get upgrade. Most
recompilations should be a no-op if the dependencies have not changed.
If they have changed the rebuild won't have been in vain.