Can you change a setting on your e-mail or browser program, to allow resizing of images?
Another option would be to save the images and then view them with an image viewer program (most of which will allow for changing the size (zoom).
If all you are doing with the images, is looking at them on your screen, then you could tell your cousin to resize them before sending them. This can also shrink the file size, making them easier to transmit. There are two main ways to change the 'size' of an image file like a JPEG. The first is to change the actual size (in pixels). For example, the image might be 2000x3000 pixels, but your screen is probably in the 1000-1400 pixel range. So if he resized the imaged to say, 800 pixels wide, they would fit nicely on your screen.
Also, when saving a JPEG, you can choose the quality/compression level. This allows you to make the file size smaller, at the cost of quality. But you can compress the file quite a bit, before the quality loss is actually visible in the image. If they are just for your amusement, he could probably knock the quality down to 50 or 60% with no problems.
If both the size and quality are reduced, the files should get very small. Perfect for E-mailing and sharing with friends, but if you want to print the images, then you will want the larger files.