Hi,
In the Window Menu is the option to open the File Transfer Window.
Does this say you have the Files ?
In the Chat they may look like place holders and have a spyglass like icon to "open" them in Preview.
It seems that AIM in particular have stopped allowing plain .jpegs and other picture formats to appear "in-line".
These may be as corrupt .jpegs have in the past been used to hide malicious code.
Try sending them in a Folder as the app will them zip these.
The iMessages account should not have this problem.
9:24 p.m. Saturday; September 5, 2015
iMac 2.5Ghz i5 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad