How to convey msg to gal s parents after not finding her pic attractive?

hii all,i m in the process of finding a suitable alliance for me.recently,after having a bit of chat between my parents n gals parents,we had asked for her snap..after getting the snap,i find her not attractive enough,,n not comfortable in proceeding any further,,now will it be ok to just convey this msg at this stage or shud i go for a personal meeting with gal n her parents with my family n then say no...i dnt want to be harsh,hw shud i politely say no n when??