tomatoe plant brown spots
Based on your photo this looks like a type of fungal leaf spot (possibly septoria) on the tomato foliage. There are several types and are frequently weather dependent and vary in severity from season to season according to rainfall and temperature. Here is more information
We also noticed aphids, a sucking insect which can cause crinkling/curling. http://extension.umd.edu/growit/insects/aphids-vegetable-garden
At this point, if the lower leaves are only affected, simply pinch off and discard in the trash. Follow tips above to prevent.