About catalog images I found smth here http://www.magentocommerce.com/knowledge-base/entry/resizing-catalog-images/.
But it has a path Design > Themes Editor > Customize (Theme) > Catalog Images that I haven’t in my admin panel.
As for product images I haven’t any idea how to resize image.
I will be grateful for any link and tips.
PS: I read out that image resize is used in the template file directly. If we have 100 images per page it means that Magento resizes 100 times per page loading. Seems it require a lot of additional resources.
I believe you’re going about this the wrong way. It is always best to retain the highest quality version. Let’s say right now you want to shrink images to 300×300. What happens next year when you redesign you site and you want to feature product images more prominently and you want 400×400 images? You can’t because you only have 300×300. As already mentioned, Magento has an resize mechanism that does exactly what you want. It will resize (shrink) the images once and store them in a cache. The first time that image is loaded then Magento does the resize and any subsequent image load will load the already saved image from the cache. Voila, you have both the original high quality image stored and the resized image stored.