Limits are in bytes like you can see in a guide of forum ad design. Byte is a common unit for limits in Bitcoin if I am right.
The maximum image size is 51200 bytes
https://bitcointalk.org/ad_design.phpAre you sure? For a long time I thought the limit was 2.5 MB
I used it as an example that it seems theymos or the forum software is keen on using bytes for limit in posts and ad banners.
About ad banners, it is limited in px too (not taller than 47px).
About avatars
It must be no more than 120px wide, 80px tall, and 100 KiB in size.
About images, you are correct, it is initially at 1.5MB, then increases to 2.5MB.
Images must be less than 1.5MB. Resize or compress your image.
OK, I increased it to 2.5.