There are a couple of things to look at first, one is whether the auto crop is turned on if using a gallery block. The trouble with that is that it will crop a picture, cut off something you don't want in order to keep it the same size as other images. You can adjust grid size, columns, if using one of them and if single image blocks, size them using spacers. But mixing landscape and Portrait together means picking your poison same size or something cropped. The latter you can adjust a bit using the centering control when editing the picture, in 7.0. That control shifts the center of the cropped image up or down.