There is a total size limit for attachments rather than a total number. The limit is 50Mb, although it's unlimited for forum supporters. (It's actually the supporter link
here that I found the limit for non-supporters on).
You can also put pictures in your gallery then link to them in your post. See the link in my signature for instructions on that. However there is a limit on gallery space as well. It doesn't say on the above link what that is, just that supporters get double. However just having looked at the gallery upload link it seems to imply I have unlimited (not currently a supporter). Not sure if that has changed, or if mine is different as a moderator
It might be worth checking that out.
Other than that, you need to put them on an external site. I get on well with Flickr which has an easy way to link to this forum (it gives bbcode which you just past into your post). It gives you 1Tb free which is absolutely masses.