I see no size reduction in the images, use tweak book to verify it for yourself. In fact all the images in the original mobi are small enough that they would not be resized even without the tablet profile.
Here are the dimensions of the image in Emma.mobi
Code:
p/input/images/00001.jpg JPEG 232x300 232x300+0+0 8-bit sRGB 15.3KB 0.000u 0:00.000
p/input/images/00002.jpg[1] JPEG 245x393 245x393+0+0 8-bit sRGB 18.5KB 0.000u 0:00.000
p/input/images/00003.jpg[2] JPEG 244x382 244x382+0+0 8-bit sRGB 19KB 0.000u 0:00.000
p/input/images/00004.jpg[3] JPEG 269x409 269x409+0+0 8-bit sRGB 21.4KB 0.000u 0:00.000
p/input/images/00005.jpg[4] JPEG 258x415 258x415+0+0 8-bit sRGB 19.9KB 0.000u 0:00.000
p/input/images/00006.jpg[5] JPEG 272x423 272x423+0+0 8-bit sRGB 19.3KB 0.000u 0:00.000
p/input/images/00007.jpg[6] JPEG 285x439 285x439+0+0 8-bit sRGB 21.9KB 0.000u 0:00.000
p/input/images/00008.jpg[7] JPEG 252x389 252x389+0+0 8-bit sRGB 20.6KB 0.000u 0:00.000
p/input/images/00009.jpg[8] JPEG 258x413 258x413+0+0 8-bit sRGB 22.5KB 0.000u 0:00.000
p/input/images/00010.jpg[9] JPEG 265x429 265x429+0+0 8-bit sRGB 20.8KB 0.000u 0:00.000
p/input/images/00011.jpg[10] JPEG 273x433 273x433+0+0 8-bit sRGB 21.7KB 0.000u 0:00.000
p/input/images/00012.jpg[11] JPEG 273x416 273x416+0+0 8-bit sRGB 17.7KB 0.000u 0:00.000
p/input/images/00013.jpg[12] JPEG 301x477 301x477+0+0 8-bit sRGB 20.7KB 0.000u 0:00.000
p/input/images/00014.jpg[13] JPEG 278x425 278x425+0+0 8-bit sRGB 18.9KB 0.000u 0:00.000
p/input/images/00015.jpg[14] JPEG 256x401 256x401+0+0 8-bit sRGB 16.5KB 0.000u 0:00.000
p/input/images/00016.jpg[15] JPEG 286x472 286x472+0+0 8-bit sRGB 19KB 0.000u 0:00.000
p/input/images/00017.jpg[16] JPEG 264x401 264x401+0+0 8-bit sRGB 21.9KB 0.000u 0:00.000
p/input/images/00018.jpg[17] JPEG 296x472 296x472+0+0 8-bit sRGB 20.9KB 0.000u 0:00.000
p/input/images/00019.jpg[18] JPEG 273x434 273x434+0+0 8-bit sRGB 21.3KB 0.000u 0:00.000
p/input/images/00020.jpg[19] JPEG 276x422 276x422+0+0 8-bit sRGB 20.4KB 0.000u 0:00.000
p/input/images/00021.jpg[20] JPEG 281x446 281x446+0+0 8-bit sRGB 17.9KB 0.000u 0:00.000
p/input/images/00022.jpg[21] JPEG 278x447 278x447+0+0 8-bit sRGB 20.3KB 0.000u 0:00.000
p/input/images/00023.jpg[22] JPEG 265x423 265x423+0+0 8-bit sRGB 20.5KB 0.000u 0:00.000
p/input/images/00024.jpg[23] JPEG 278x435 278x435+0+0 8-bit sRGB 21.2KB 0.000u 0:00.000
p/input/images/00025.jpg[24] JPEG 501x800 501x800+0+0 8-bit sRGB 74.7KB 0.000u 0:00.000
p/input/images/00026.jpg[25] JPEG 150x240 150x240+0+0 8-bit sRGB 12.1KB 0.000u 0:00.000
p/input/images/calibre_cover.jpg[26] JPEG 501x800 501x800+0+0 8-bit sRGB 74.7KB 0.000u 0:00.000
and here are they for Emma.epub
Code:
images/00001.jpg JPEG 232x300 232x300+0+0 8-bit sRGB 15.3KB 0.000u 0:00.000
images/00002.jpg[1] JPEG 245x393 245x393+0+0 8-bit sRGB 18.5KB 0.000u 0:00.000
images/00003.jpg[2] JPEG 244x382 244x382+0+0 8-bit sRGB 19KB 0.000u 0:00.000
images/00004.jpg[3] JPEG 269x409 269x409+0+0 8-bit sRGB 21.4KB 0.000u 0:00.000
images/00005.jpg[4] JPEG 258x415 258x415+0+0 8-bit sRGB 20KB 0.000u 0:00.000
images/00006.jpg[5] JPEG 272x423 272x423+0+0 8-bit sRGB 19.3KB 0.000u 0:00.000
images/00007.jpg[6] JPEG 285x439 285x439+0+0 8-bit sRGB 21.9KB 0.000u 0:00.000
images/00008.jpg[7] JPEG 252x389 252x389+0+0 8-bit sRGB 20.6KB 0.000u 0:00.000
images/00009.jpg[8] JPEG 258x413 258x413+0+0 8-bit sRGB 22.5KB 0.000u 0:00.000
images/00010.jpg[9] JPEG 265x429 265x429+0+0 8-bit sRGB 20.9KB 0.000u 0:00.000
images/00011.jpg[10] JPEG 273x433 273x433+0+0 8-bit sRGB 21.8KB 0.000u 0:00.000
images/00012.jpg[11] JPEG 273x416 273x416+0+0 8-bit sRGB 17.8KB 0.000u 0:00.000
images/00013.jpg[12] JPEG 301x477 301x477+0+0 8-bit sRGB 20.7KB 0.000u 0:00.000
images/00014.jpg[13] JPEG 278x425 278x425+0+0 8-bit sRGB 18.9KB 0.000u 0:00.000
images/00015.jpg[14] JPEG 256x401 256x401+0+0 8-bit sRGB 16.5KB 0.000u 0:00.000
images/00016.jpg[15] JPEG 286x472 286x472+0+0 8-bit sRGB 19KB 0.000u 0:00.000
images/00017.jpg[16] JPEG 264x401 264x401+0+0 8-bit sRGB 21.9KB 0.000u 0:00.009
images/00018.jpg[17] JPEG 296x472 296x472+0+0 8-bit sRGB 21KB 0.000u 0:00.000
images/00019.jpg[18] JPEG 273x434 273x434+0+0 8-bit sRGB 21.3KB 0.000u 0:00.000
images/00020.jpg[19] JPEG 276x422 276x422+0+0 8-bit sRGB 20.4KB 0.000u 0:00.000
images/00021.jpg[20] JPEG 281x446 281x446+0+0 8-bit sRGB 17.9KB 0.000u 0:00.000
images/00022.jpg[21] JPEG 278x447 278x447+0+0 8-bit sRGB 20.3KB 0.000u 0:00.000
images/00023.jpg[22] JPEG 265x423 265x423+0+0 8-bit sRGB 20.6KB 0.000u 0:00.000
images/00024.jpg[23] JPEG 278x435 278x435+0+0 8-bit sRGB 21.2KB 0.000u 0:00.000