That's very interesting! I converted the prices to be in the same units and did some calculations for better comparison.
Linode
Cost per day: $0.65
Time per image: 15.2
Images per day: 5684.2105263158
Cost per image: $0.0001143519
Images per dollar : 8744.9392712551
Storm-on-demand
Cost per day: $1.2
Time per image: 13.05
Images per day: 6620.6896551724
Cost per image: $0.00018125
Images per dollar : 5517.2413793104
EC2-micro
Cost per day: $0.84
Time per image: 168
Images per day: 514.2857142857
Cost per image: 0.0016333333
Images per dollar : 612.2448979592
EC2-small
Cost per day: 2.16
Time per image: 63
Images per day: 1371.4285714286
Cost per image: 0.001575
Images per dollar : 634.9206349206
EC2-medium
Cost per day: $4.464
Time per image: 12.13
Images per day: 7122.8359439407
Cost per image: 0.0006267167
Images per dollar : 1595.6173709545
Linode Cost per day: $0.65 Time per image: 15.2 Images per day: 5684.2105263158 Cost per image: $0.0001143519 Images per dollar : 8744.9392712551
Storm-on-demand Cost per day: $1.2 Time per image: 13.05 Images per day: 6620.6896551724 Cost per image: $0.00018125 Images per dollar : 5517.2413793104
EC2-micro Cost per day: $0.84 Time per image: 168 Images per day: 514.2857142857 Cost per image: 0.0016333333 Images per dollar : 612.2448979592
EC2-small Cost per day: 2.16 Time per image: 63 Images per day: 1371.4285714286 Cost per image: 0.001575 Images per dollar : 634.9206349206
EC2-medium Cost per day: $4.464 Time per image: 12.13 Images per day: 7122.8359439407 Cost per image: 0.0006267167 Images per dollar : 1595.6173709545