Did you place the images on the phone itself or on the SD card? I ask because if your gallery is only set up to view one or the other (or even your online images) then you may not see the images you downloaded.
Also, depending on the directory you put it in, it may not show up. On most devices you need to put the images (if putting them on the device itself) in ... "Phone" ... "Pictures"...then you can have them in that main folder, or in sub folders. If you did not put them there, or in a folder that the gallery is set up to view, you won't be able to see them.
Check your gallery settings.