Yes there is!
You need to create a "Smart Folder" (ie a saved search). Easy peasy.
1. In Finder, create a new Smart Folder (File -> New Smart Folder).
2. Click on the + key on the far right, choose "Kind" is "Image" and (if you like) the particular format of image desired (or just "All").
3. Press the little + symbol on the far right of the "Kind" line to add additional criteria, select "Other" and from that last choose "Resolution height" then the default "equals" and then type in "90".
4. Repeat step 3, only choosing "resolution width" this time.
5. Press the "Save" button and name the Smart Folder something like "90x90 images."
This search will automatically recompile a list of all files on the hard drive that meet this criteria every time you open the Smart Folder. You can relocate this folder anywhere you'd like. It sounds like a lot more work than it is, it's easy and amazing what you can do with images and Smart Folders!
