I spent some time looking for some images from Obama's rallies. Evidently the media very seldom provides pictures of the crowd size, as they are small compared to Trump's rallies.
The same media is also reluctant to show the size of the crowd at the Trump rallies, because it reinforces the slant that "Trump is unpopular."
Obama's handlers also have a habit of booking him into small venues, so they can push the narrative that he "packed" the place. They also sell a limited number of tickets, so they can claim that the rally is "sold out."
For example, Obama's rally in Georgia was in basketball stadium at Morehouse college. The maximum capacity there is only 6,000 people. And in every rally Obama does, the cameras always keep a tight shot of the podium, so you can't see how small the crowd is.
In addition to that, Obama's handlers run Craigslist ads a week or two before his rallies. The ads typically offer people the sum of $15 for attending the rally. Here is a screen cap of the Craigslist ad posted before the November 2nd rally:
Now just for shits and grins, let's compare the sizes of Obama's rallies to Trump's. Here is a shot from the back of the room, when Obama spoke in Miami, for Gillum and Nelson:
Whereas Trump's rallies tend to look more like this one...