What size should TabBar images be?

30x30 is points, which means 30px @1x, 60px @2x, not somewhere in-between. Also, it's not a great idea to embed the title of the tab into the image—you're going to have pretty poor accessibility and localization results like that.

According to the Apple Human Interface Guidelines:

@1x : about 25 x 25 (max: 48 x 32)

@2x : about 50 x 50 (max: 96 x 64)

@3x : about 75 x 75 (max: 144 x 96)