Suppose that our thumbnail image is 1000x1000 pixel although it should be 133x100 pixel, magento automatically will re-size it and show the re-sized image on the page, I know that it can slow down the website when we have large images, but I want to get an official answer of:
Yes, it slows down the website even when magento has re-sized images.
I need to know the reasons why it is best to have the images smaller. the reason which I can think is that the KB of an image even when the re-sizded one has been shown is more than when it is smaller, moreover resizing make magento to process the resize which means adding load on the website.(I don't know if it will be processed once or each and every time?)
Does the resizing happens once when we are uploading the image or does it take place everytime we need to see the image on the page?
as an example I have uploaded one large image which has been resized in a static block, when I go to the image url although I am seeing the resized one, I can see that the source URL still has the bigger image which means it can lower the performance of the website.
I need to bring more reasons to convince our team to go through thousands of products and update the images,I appreciate any help on this.