Assuming it takes you at least 1-2 hours per design (and even with mad photoshop skillz it's unlikely it'd be much shorter than that), you're probably better off getting an office job somewhere, or even maybe a burger-flipping job. Given all the additional expenses of running your own business, this is probably not a viable business model (i.e. you will lose money on the whole).
The only way this would be justified is if you use this as a source of clients to up-sell more expensive work to.
The only way this would be justified is if you use this as a source of clients to up-sell more expensive work to.