Most facilities allow photos that are suggestive without being explicitly sexual, and panties and bra generally fall within that line as long as nothing is fully exposed. The standard that most mailrooms apply is whether private parts are covered. Tasteful lingerie photos, the kind you would see in a mainstream retail catalog, typically pass without issue at the majority of facilities.
That said, every facility sets its own policy and some are stricter than others. County jails tend to be more restrictive than state prisons. Federal facilities follow Bureau of Prisons guidelines which prohibit sexually explicit material but generally permit photos that are suggestive without being graphic. Some facilities ban any photo they consider provocative regardless of what is technically covered, and the mailroom officer making that call has significant discretion.
Before sending anything, it is worth knowing the specific policy at his facility. A photo that gets rejected does not just fail to arrive. In some facilities it gets flagged, documented, and can create unnecessary attention on his housing unit or record. It is not worth the risk of sending something that crosses a line you did not know existed.
The safest approach is to keep it tasteful, make sure nothing explicitly sexual is visible, and avoid anything that could be interpreted as pornographic. Photos sent through InmateAid go through USPS like any other mail and are subject to the same facility mailroom review as anything else that arrives. When in doubt, err on the side of a little more coverage rather than a little less.