So... let me get this straight, you take pictures with a camera, then move it to the tablet? And then when you can use your external HDD you then use move the pictures to there?
It's possible, you need a tablet with OTG support. You then need a micro USB to SD card reader as nearly all tablets don't have SD card support (just micro SD), and an OTG cable to connect the tablet to the external HDD.
EDIT: Scrap that, here's a better idea. Get a micro SD card with an SD card adapter, then that avoids the need of an SD card reader as you can insert the SD card straight into both devices.