Theme doesn't detect batch resized images!

I have changed my websites theme. Image sizes are different than my previous theme. New theme look for resized image and shows it, if didn’t found, it shows raw uploaded image.
So I had two option to make my uploaded images fit new theme:
1) Deleting them and uploading again which is really hard!
2) Using a PHP script to resize and crop images to new sizes.

I tried option 2 and resized all images with new identifier (ImageName-390×90.png) but even though all of the images were successfully resized, the new theme doesn’t detect my resized images 🙁

I think in somewhere in database, posts are marked to have a thumbnail it the specified size. What should I do?