We are converting a magazine to Kindle which has full page images. We have converted all the full page images to 884 x1243 pixels all images look same sized when converted to Mobipocket file format. After the Mobipocket file is uploaded in Kindle preview, the problem is that images are showing of different sizes. Is this the problem with the preview or file?
don't trust the DTP previewer - it's notoriously bad for displaying images (they usually appear too small). if the file looked fine in mobi format, you should be okay for the kindle.
one note, however: your images will be resampled and downsized automatically by DTP to fit into the maximum dimensions of 450px wide x 550px high. so if your images have a lot of detail (particularly text), please keep that in mind - you'll lose a lot of resolution. it also only has something on the order of four grayscale tones, so images that don't have very strong contrast usually look very washed out.