the attachments and hotlinked images are now constrained to an initial display of 600x600. if a linked image is larger than that, a dialog box will appear on top of the image to let you know. if an attachment is larger than 600x600, clicking on the image itself will expand it to the larger size. this should make it easier to load threads due to the uniformity of the images. you are not required to resize your images any differently than you are currently doing.