I don't really have that problem. I mostly use either png's (screenshots) or jpeg's (photos). You could certainly run into that problem if you're dealing with lots of formats or with other peoples files.

My intent is for this to give you solid starting points to work from in some situations. Individually these commands were first written for myself and published online. Those pages became somewhat popular, like people were looking for some specific examples. So, I thought I'd try combining them and see if people found it useful enough to encourage me to spend the time to expand the list into something more.